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What level of radiation is safe for a granite countertop? Using existing laws in the US, we were able to come up with some levels that might apply.

First off is a paper outlining what various states use for NORM, Normally Occurring Radioactive Material, found in the oil and gas industry. The industry seems to have an exemption allowing higher levels of radiation. From 5 pCi/g to 30 pCi/g is the range, with almost all states using the lower figure of 5 pCi/gram.

Oil and Gas equipment is allowed to be used if under 50 to 25 uR/hr above background. Gamma measurements are used because they are simple to take and inexpensive. Dose limits are taken from the IRCP and the NCRP recommended levels of 1 milliseivert per year (100 millirem per year), but both organizations recommend that the upper level should never be met, expected doses should be much less than the limit.

On yearly limits, NCRP says that anything over 5 times the yearly normal background radiation (100 millirems) needs to be mitigated, but they warn that ALARA principles should always be followed, that the goal should be significantly lower radiation than the allowed levels.
The paper concludes by recommending that levels be set at the ICRP levels of 50 pCi/g (47.5 uR/hr) for contaminated pipe and equipment, and waste and 15 pCi/g (14.25 uR/hr) for sludge and waste particles such as stone cuttings from the drilling of wells.

For remediation work such as salvaging or cleaning equipment to lower the radiation levels, the committee set a level of 30 pCi/g (28.5 uR/hr) exposure at which permission from the authorities must be obtained. They insist that some public good must come by the exposure, such as cleaning up a contaminated site, to justify the risk to the workers during cleanup.

You can view the original document here

http://www.osti.gov/bridge/servlets/purl/750593-B3YgBx/webviewable/750593.pdf

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Another source is the EPA Project Summary that was written for the state of Florida on allowed levels of radiation in concrete for use in homes.
This study recommended the concrete was lower than 5 pCi/g (4.75 uR/hr) and that no material over 10 pCi/g (9.5 uR/hr) is used as a material.
This level may well be unobtainable by many of the granite types available. The lowest radiation level granite we have found is Absolute Black, with around 5 uR/hr after background levels are removed.
You can view the original document here
http://www.p2pays.org/ref%5C07/06324.pdf
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This document details a survey of an area contaminated by Gamma radiation. Measured at a level of three feet off the ground, averaged levels of 13.8 uR/hr, with hot spots up to 27.5 uR/hr.

The study said this,

“radioactive contamination is defined as exceding the normal ambient gamma radioactivity level at one meter height by more than 5uR/hr — the criteria limit for this project.”

The original document is here

http://www.etec.energy.gov/library/D&D_page/N704SRR990034_FSDF_Baseline_Survey.pdf

June 10th, 2008
Major break through today on setting safe levels for granite countertops. A few weeks ago, Christina, my better half, contacted the EPA asking about granite slabs with specific levels of radiation.

They responded by asking for more time, then about a week ago, they responded by changing their online position on Radon and granite countertops, recommending that granite countertop owners have their homes tested for Radon.

Today, we received further information, including some info on what is considered a safe level of radiation in granite.

Below are some exerts from the letter, with the entire letter posted at the end of the article.

“The available data on the contribution of radon emissions from granite countertops to the indoor air level in homes is too inadequate to allow us to comment about it at this time.
While most granites used for building stone may not be considered harmful from a radiological viewpoint, some granitic deposits in the U.S., Canada, and elsewhere in the world, as you pointed out, host economically recoverable concentrations of uranium ore.”
So there it is, official proof that high radiation level granite countertop slabs can be qualified as containing Uranium ore.

Due to the economics of extraction, miners searching for uranium in granitic rock tend to look for concentrations primarily in intrusive veins or pegmatites. These ore bodies tend to be distinctive looking and separate from other parts of the surrounding “country rock” granite–this is the case for Namibian deposits for example. It is possible that enrichment could be found in adjacent host rocks, as either outliers of the commercial ore zones or an increase in naturally occurring radioactive minerals in the “country rock” used by quarries. However, most prudent mine claims, leases, or license boundaries are located if possible outside the mine able zones to ensure that current and potentially future economic resources are captured by the operation.

Dr. Hans Hensel stated on Garden Web a few days ago, that granite with veining pegatites were in high demand as countertop slabs, and that they were distinctive and unusual looking. The rest of the paragraph talks about the normal process of drilling core holes and mapping the Uranium deposits so that maximum use of the mining claim is taken. Outliers are dykes or veins that continue outside the main areas of ore.

“See Table 1.3 of our uranium report, volume 1, http://www.epa.gov/radiation/docs/tenorm/402-r-08-005-voli/402-r-08-005-v1.pdf which illustrates the average naturally occurring radionuclide concentration values for igneous and sedimentary rocks, but this does not include the variations in range for each. The numbers below would not cause concern in a well-ventilated kitchen. “

The link seems to be broken for now, but here is the granite portion of that table.

All data in pCi/g
EPA average content for granite in table 1.3 in your Uranium Report.
EPA figures RA 226 1.3 U 238 1.3 TH 1.3 K 40 22
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Sample M RA 226 986.95 U 235 37.83 TH 144.76 K 40 53.96

Sample N RA 226 312.82 U 235 13.145 TH 36.92 K 40 30.139
Sample O RA 226 156.6 U 235 5.143 TH 22.458 K 40 37.912

Samples M through O are content levels in samples tested from a Bordeaux countertop that was removed earlier this year due to Radon hazards.

As you can see, all three samples from that Bordeaux countertop were much, much, higher than what the EPA said is average. Hundreds of times higher in some cases. You can also see that despite MIA expert Dr. Hans Hensel claims that most of the radiation in granite countertops comes from Potassium 40 ( K 40), in fact most of the radiation comes from Radon and Thorium.

“Assuming that the readings were accurate, a measurement of 7 micro Roentgens (microR) per hour would be considered a background reading from average soil and rock samples as naturally occurring radionuclides are found in most everything. The much higher readings you cite from the Brazilian sample and Tacoma slab, if accurate, could, under certain circumstances, pose a problem however for some people. The exposures would have to be continuous (e.g., hours per day) and prolonged (e.g., years) in order for there to be a significant increase in risk. The higher the exposure, the less time would be needed to create a higher risk. “

The readings are accurate, we had three of the same meter measuring the Niagara Gold slab, and all read the same. A check source came with our Leni Geiger counter, and the meter was calibrated before shipping by an expert in the field. In addition, a radiation enthusiast used his other methods of measurement to confirm that our meters were accurate and calibrated correctly. We find the questioning of the levels understandable, in this case, this expert had no idea that such radioactive granite countertop slabs were being imported. Note that the EPA expert said that “could, under certain circumstances, pose a problem however for some people.

“Data at this time is inadequate to characterize the radiation risk posed to individuals who spend extended periods of time in close proximity to countertops with the elevated levels of radiation as you describe. “

So there it is, even the EPA says that the radiation risks are unknown…… This is not good.

“Federal and state agencies generally provide controls for exposures of members of the public to radioactive substances. Without going into a lot of detail on this topic, EPA and some State agencies have used an exposure of 20 microR/hour as a remediation action level for entire rooms, homes or buildings. Any review of the contribution of countertops to overall dose from radiation and radon in a home would examine, among other factors, time spent in a kitchen versus other living and sleeping areas, which minimizes the exposure from a single source such as a countertop. “

Early on, after getting our meters, I chose 20 uR/hr as an arbitrary level of radiation that a hunch told me was the dividing line between good granite and dangerous granite. Turns out that I was pretty close. Much of the “hunch” came from reading for months on this subject, some of it must have soaked in.

Twenty microRems per hour is written as 20uR/hr. In the coming days, as our radioactive granite data gets posted, you can use this figure to put readings in perspective. One thing, though, they using this figure not on contact as we are, they are holding the meter about 3 feet off the ground. So to get exact figures, we will need to start measuring 3 feet away from the slab. And some granites will exceed this, as much as 150 uR/hr at three feet in the case of Four Seasons.

The rest of the letter is about fabrication shops like ours, the dangers from working a high level granite and the steps we should take to prevent problems. After reading that section, one wonders why the granite industry generally wants to derail the testing effort. It seems they and their employees have more to be afraid of than homeowners in most cases.
We will be replying tomorrow, outlining our check sources and quality control methods used in testing, as well as asking if the Juparana Bordeaux countertop was a risk to the homeowners before it was removed.

Here is the emai from the EPA, I removed the authors contact info so he doesn’t get a bunch of hate mail.

Dear Ms. Weigel,
Thanks for sending all this research information. I will try and address your concerns.

Uranium, radium, and thorium are natural constituents of the wide number of mineral species occurring as crystals which can be found in granites from around the world. Some granites are more radioactive than others, depending on the geothermal fluids present in the matrix which then cooled to form the mineral grains.
The presence of radium and thorium in the mineral matrices can decay into radon which may be released over time through radioactive decay. The presence of these minerals in an igneous rock matrix (which includes granites) rather than sediment acts to decrease the radon flux rate however. The available data on the contribution of radon emissions from granite countertops to the indoor air level in homes is too inadequate to allow us to comment about it at this time.

While most granites used for building stone may not be considered harmful from a radiological viewpoint, some granitic deposits in the U.S., Canada, and elsewhere in the world, as you pointed out, host economically recoverable concentrations of uranium ore.

Due to the economics of extraction, miners searching for uranium in granitic rock tend to look for concentrations primarily in intrusive veins or pegmatites. These ore bodies tend to be distinctive looking and separate from other parts of the surrounding “country rock” granite–this is the case for Namibian deposits for example. It is possible that enrichment could be found in adjacent host rocks, as either outliers of the commercial ore zones or an increase in naturally occurring radioactive minerals in the “country rock” used by quarries. However, most prudent mine claims, leases, or license boundaries are located if possible outside the mineable zones to ensure that current and potentially future economic resources are captured by the operation.

See Table 1.3 of our uranium report, volume 1, http://www.epa.gov/radiation/docs/tenorm/402-r-08-005-voli/402-r-08-005-v1.pdf which illustrates the average naturally occurring radionuclide concentration values for igneous and sedimentary rocks, but this does not include the variations in range for each. The numbers below would not cause concern in a well-ventilated kitchen.

Radiological testing of imported, or domestic, granite is not a common practice. There have been numerous studies on the contribution of building stones to background radiation, and some limited studies on comparisons of radiological levels between different granites.

One problem in conducting the research you cited is that radiation detectors must be checked against a source of a known radiation level (check source) to verify that its readings are accurate. The divergence in numbers you cited for the Brazilian sample using different machines suggests checking their accuracy might be useful. Assistance from geologists, health physicists, or other licensed radiation professionals would be helpful in this instance–you might want to inquire at Oklahoma State University, or the Oklahoma Department of Environmental Quality’s Radiation Management Section, both in Oklahoma City, for example.

Assuming that the readings were accurate, a measurement of 7 microRoentgens (microR) per hour would be considered a background reading from average soil and rock samples as naturally occurring radionuclides are found in most everything. The much higher readings you cite from the Brazilian sample and Tacoma slab, if accurate, could, under certain circumstances, pose a problem however for some people. The exposures would have to be continuous (e.g., hours per day) and prolonged (e.g., years) in order for there to be a significant increase in risk. The higher the exposure, the less time would be needed to create a higher risk.

The dose of radiation an individual receives is based on the amount and types of radiation (gamma, alpha, beta for example), distance to the radiation source, shielding (useful primarily for alpha or beta radiation, not so much for gamma), and time of exposure. When measuring the dose rate with a meter, health physicists will examine the radiation level both at the source, and at a distance (in a room’s center for example, with the measurement at waist level) to more objectively portray the likely exposure of an individual. Data at this time is inadequate to characterize the radiation risk posed to individuals who spend extended periods of time in close proximity to countertops with the elevated levels of radiation as you describe.

Federal and state agencies generally provide controls for exposures of members of the public to radioactive substances. Without going into a lot of detail on this topic, EPA and some State agencies have used an exposure of 20 microR/hour as a remediation action level for entire rooms, homes or buildings. Any review of the contribution of countertops to overall dose from radiation and radon in a home would examine, among other factors, time spent in a kitchen versus other living and sleeping areas, which minimizes the exposure from a single source such as a countertop.

Occupational exposures to stone cutters, cabinet or carpentry employees is another concern. In such instances, the potential for increased direct radiation, inhalation, and ingestion of particles as well as radon gas might be increased in shops where large amounts of stone with elevated levels of radiation are stored and worked. There are a few immediate courses of action you may be able to take. The first would be to take radon measurements in the workplace with charcoal canisters (generally available at larger hardware stores or online) or other radon detectors. If so, place them in accordance with the manufacturer’s/laboratory instructions in locations likely to be accessed by workers (though probably not on top of one of the suspect granite slabs). Also, carefully follow the instructions on handling, packaging and returning the devices for analysis. Although EPA does recommend an action level of 4 picocuries/liter of air for homes, schools, and a few industries (drinking water treatment and sewage treatment plants), you may wish to consider the advisability of increasing indoor ventilation should your own readings equal or exceed that level. Secondly, consider having a licensed health physicist conduct a radiation survey of your shop and make recommendations on health and safety practices to minimize worker exposures to radiation. Again, the Oklahoma Department of Environmental Quality’s Radiation Management Section may be able to provide you with some additional guidance or list of qualified radiation specialists.

I hope this information is helpful. Please contact me if you have any further questions.

(Mr.) L S

Geologist
U.S. Environmental Protection Agency

1200 Pennsylvania Ave., NW
Washington, DC 20460

Lots of discussion about granite countertops, Radon, and radiation. Homeowners are wondering who to believe or what to do if they have a granite countertop.

The bottom line for most people on this issue is how dangerous or how safe is my granite countertop. This has been a difficult question to answer, many variables need to be taken into consideration, dose rates converted into existing risk factor units, difficult to do quickly.

But, today we found a handy Risk Calculator on a nuclear site. You can insert the radioactive reading of your granite top in what ever units the meter reads in, set the number of hours you spend near or in the kitchen, the occupancy length, and chose to use the public or worker Risk Factor. For now, lets consider Gamma only, since we are concentrating on that risk because it is easy to measure and is indicitive of the Radon emission.

Using 41 uR/hr (Class A max), 2 hours per day in or near the kitchen, 365 days per year, a lifetime occupancy, and the public Risk Factor, the extra cancer rate is 1 in 893 people exposed. Lots of granites in this range.

Using 20 uR/hr, same factors, 1 extra cancer in 1832 people exposed.

Using a hot slab, 100 average reading across the slab, 1 extra cancer in 366 people exposed.

Using a very hot slab, 150 uR/hr average reading across the slab, 1 extra cancer in 244.

So low level stones like Uba Tuba, Black Pearl, Absolute Black, the extra cancer cases will be between 1 in 1832 and 1 in 3660 people.

If we add the Alpha and Beta to the Gamma, things get pretty scary.

Verde Peacock, 500 uRhr, 1 extra cancer in 73 people exposed.

Bordeaux, 1.7 mR/hr, 1 extra cancer in 21 people exposed.

Niagra gold, 5.1 mR/hr, 1 extra cancer in 7 people exposed.

Four Seasons, 13.1 mR/hr, 1 extra cancer in 2.8 people exposed.

Savanah, 17 mR/hr, 1 extra cancer in 2 people exposed.

Keep in mind that spending more time in the kitchen will change these rates upward.

Even the low level slabs, at 1 in 3,660 , will affect a large number of people. Assume that 30 million people have low level granite countertops in their homes, 8,196 extra cancer cases will result assuming 2 hours per day use of the kitchen, using Gamma exposure only, no Radon, Alpha, or Beta.

Eight thousand, one hundred ninety six extra cancers cases…..

If you want to know the danger to children, change the Risk Factor in the public box to .08 to reflect childrens extra risk from radiation.

Using 41 uR/hr Gamma only (class A limit), 2 hours per day, and five years exposure, expect 1 extra cancer in 7,817 children exposed.

For infants, use .09 for the Risk Factor in the Public box to reflect an infants extra risk from radiation. .

For an infant, using our Class A stone of 41 uR/hr Gamma only, 2 hours per day and 5 years exposure figure 1 extra cancer in 6,949 infants exposed.

For an Infant, using Bordeaux, 1.7 mR/hr of ALpha, Beta, Gamma, 2 hours per day and 5 years exposure, figure 1 extra cancer in 167 infants exposed.

RISK CALCULATOR LINK

The MIA reopened the debate this week, sending a guy that they have used before to blast the competition, Dr. Hans Hensel. Dr. Hans wrote a piece for the MIA back in 2005 that was so one sided that the industry trade journals refused to publish it. This “white paper” on Quartz was full of holes. He took one instance of a marble based engineered stone, and used it to attempt to smear the quartz industry.

In the latest missive, Dr. Hans attacks Dr. Llope for suggesting testing of slabs prior to use. His position seems to be that only he is qualified to test natural stone, that doin a simple survey with a radiation meter is not good enough. His concerns seem to be that, well, no one really knows what he objects to. He just says that nuclear physicts waving meters around won’t do at all. Go figure. I wonder if he has a plumber change his toilet paper roll.

Here is the reply I posted, not sure how long the post will stay up. Garden Web banned me last year for daring to talk about the granite/radiation issues, and though they allowed me to re register tonight, it might be just an oversight.

Forgive the tone I took. I see Dr. Hans as just a shill for the stone industry. I think that most will understand that I believe supressing the testing effort will and has lead to harm to consumers and massive liability to the countertop trade.

The battle for the truth, Garden Web style

Dr Hans,
First off, allow me to concede your expertise in Geology. You are indeed well known in the stone industry, congratulations on your accomplishments in your lifetimes work. That said, after following the previous thread on this issue and reading many posts saying that no one related to either side of the fight should be relied upon, why should consumers look upon your info as unbiased?
If I may, I’d like to go through your post paragraph by paragraph so that others can mark the place in the debate. Your arguments contain many instances of Argumentum ad ignorantiam, Converse accident, Amphiboly, Non sequitur, and Tu quoque arguments. An experienced debator will easily poke holes in your positions. The rest of you, look em up….
First off you wrote:
“In all these responses there was one very conspicuous void – that of a qualified geoscientist who has the scientific and technical background and who has been intimately involved in the stone industry for many years. ”
In light of that, how does your stone expertise allow you to measure the health risks of a very hot granite countertop? Would not someone who has been “intimately involved” in the stone industry bring along a strong bias for those who have paid his salary for many years? Would not a Nuclear Physicist like Dr. Llope, who is relying upon his yearly radiation safety training to determine the health risks of the hot granite countertops, be more unbiased? Not attacking your reputation, just asking you to step back and look at this from the eyes of a consumer. Does your “intimate” relationship with the stone industry barr you from claiming lack of bias or standing to gain personally from knocking down this discussion?
Then you wrote:
“The issue of radiation in granite and the emission of radon from the granite kitchen countertops has been raised a number of times over the last 15 years and there seems little doubt that the issue this time was also prompted by the quartz surfaces and plastic industry who are continually attempting to undermine the qualities/virtues of natural stone by misinformation crusades. ”
Could a consumer also look at your participation here as another “misinformation crusade”?
Then you wrote:
“By publicly suggesting that kitchen countertops might be radioactive invariably elicits a degree of concern and panic among uninformed consumers. Consumers have neither the means to determine the radiation levels in their homes nor any avenue by which they can extract such information from the fabricators or wholesalers of stone. However, they can purchase relatively cheap radon meters and undertake a crude investigation of the radon gas levels in various parts of their homes.”
Are you saying by the first sentence that should a hot granite countertop be discovered (in this case, one of the previous homeowners developed a brain tumor), that this information should be withheld from consumers? Do they not have the right to know of any potential risks? Should we rely upon the stone industry to take care of these problems?
Your second sentence, how refreshing to read that the fabricators and wholesalers of natural stone are not able to inform consumers of the radiation levels in their products. From one with an “intimate” relationship with the stone industry, can you tell me why this is the case? Why are stones not tested for safety prior to bringing them to market? One would think that this would be a nice business opportunity for your company?
Next you wrote:
“Before addressing some of the individual issues let me emphasize that the accurate determinations of radioactivity in a stone, the radiation flux and the concentration of radon in the air are not straight-forward and are prone to large errors and subsequent misinterpretations. The values can also be manipulated and grossly overstated.”
I agree with you completely. However, would you also address the issue of whether or not the values can also be grossly understated? Is not the MIA position of only 5 to 10 uR/hr radiation from granite grossly understated?
Next you wrote:
“One of the most significant misinformed statements that can be made in this debate is to tar all granites with the same brush. There are about 2700 “granites” on the world market coming from dozens of countries. In the international stone trade the term “granite” is used very loosely. It is essentially a mercantile term embracing all those stones that have an igneous mode of formation, a high degree of crystallinity, and interlocking textures which resulted from an elevated thermal history that has approached or exceeded the melting point of the rock. The term includes “black granites”, true granites, the “general” granites, pearl granites, pegmatites, anorthosites, charnockites, gneisses, migmatites and a number of exotic varieties.
For example, the term “black granite” often causes some consternation among purists, academics and those not intimately associated with the stone industry. The two terms, in the strict sense, are contradictory. Granites in the broad sense are dominated mineralogically by subequal amounts of quartz, alkali feldspar, and plagioclase feldspar, which commonly collectively comprise around 90% of the rock and give them a light colour. Relatively small amounts of dark-coloured biotite and/or amphibole provide additional descriptors (e.g. biotite granite). Black granites usually contain little or no quartz, rare alkali feldspar, and typically much more-calcic plagioclase feldspar. Biotite and amphibole are usually present in only small to trace quantities; instead, calcic pyroxene and, less-commonly, Ca-poor pyroxene dominate the ferromagnesian mineral assemblage. Apart from these fundamental mineralogical differences there are many other gross differences between “true” granites and “black” granites, and indeed between any of the broad categories named above.”
Excellent information, but perhaps you wrote this for the Regency Web site on granite some time back, it seems to be copied and pasted directly from that page, with the exception of the first few lines. Excellent example for the green movement, save those 1 and 0’s. Digital waste is growing….
But I digress.
Now, your first line claims that all granites are being tarred with the same brush. Yet Dr. Llope was on record specifically not revealing the name of the stone in the story, to prevent the stone from getting a bad reputation. Nor has anyone to my knowledge ever said that all granite were bad, indeed the consensus from the Chinese scientific community seems to be that only 20% of the stones tested fail the Class A standard. That is hardly “tarring” all granite, is it? Others like myself hold the position that less than 20% are of concern.
Would you care to defend that claim, that all stones are being “tarred with the same brush”?
Perhaps the passion to defend your product lead to over exuberance on that one sentence?
Next you wrote:
“Basically every occurrence of granite (used from here in the broad sense of the word) is unique. The uniqueness stems back to its mode of formation including the history of the original source material, the chemistry of the magma, the oxidation state, temperature, and both the intrusive and post-intrusive histories of the magma. Once intruded and emplaced numerous geological and chemical processes can subsequently modify the original composition, mineralogy and texture of every granite. Much of the modification is a function of temperature and fluid activity, both of which have naturally occurring gradients. These variations lead to a range of different stones even over the scale of tens of meters. Geologically, young granites tend to be fairly simple mineralogically and texturally compared to many granites that are an order of magnitude older. It is worth noting that most unusual or “different” granitic rock types available on the world market (in terms of colour and texture) are at least Proterozoic or older (generally older than 1.5 billion years).”
Excellent, the first sentence shows the need to test ALL slabs of granite. I agree that a few meters will lead to a different variation. I have seen sister slabs in bundles vary remarkably from other slabs, despite being less than 2″ away when sawn from the stone block. I appreciate the info on the young granite, perhaps that is why we are finding that stones like Uba Tuba are more consistent in radioactive content. I would like to mark your statement that says the most unusual or “different” granites are indeed of the older variety.
Will you concede that due to the variation, all slabs would need testing?
Next :
“The idea of conducting tests on a single piece of granite countertop that might have been quarried several years ago from an area in the quarry or other location long abandoned is naïve at best. A value obtained from a test done on one slab does not necessarily become a characteristic of that granite. If a testing regime for radiation on a particular granite type is to ever be conceived it must be done with a rigorous geoscientific control of the granite pluton, its mineralogy and chemistry, and its setting. Without this fundamental geological information the value of any testing is next to meaningless. Even then, any testing that is done might still only be valid for that small section of the quarry.”
Again you make the case for testing each and every single slab, or each block at the minimum. However, you must admit that testing the slab about to go into a new granite countertop would eliminate any hot spots or hot granites from being used, must you not? And, as in this Houston case, a homeowner may well have developed a brain tumor partially because of the radiation from this unusually hot granite countertop, would not a homeowner benefit from knowing the level of radiation from THEIR granite countertop? I do agree that that doesn’t mean that the neighbors granite of the same type is guaranteed to be unsafe, but would you say that it means that that neighbor’s granite countertop should be tested?
The rest of that paragraph has me thinking that your opinion is that unless rigorous geoscientific control of the testing of the granite slabs is done, no granite can be proven safe for use. If so, I applaud you for your honesty.
Next:
“Another elementary omission from the debate has been any discussion of the mineralogy of the different granites and how this has a bearing on the radiation issues. Reference was made to uranium ore being the cause of elevated readings of radioactivity. Although there was no intention to mislead the suggestion that there is uranium “ore” in a commercially available granite kitchentop is nonsense. If the granite body contained uranium ore it would not be a commercial dimension stone operation. Elevated concentrations of uranium in granite sufficient to be termed “ore” result in very unusual colours and textures (such as those at Roxby Downs, South Australia) in which the radiation has resulted in feldspar that has become almost black.”
Dr Llope posted a Gamma spectrometry graph of one of his granite samples, it showed Uranium, Thorium, and Potassium as being the sources of radioactivity of the stone. Are you saying that none of these elements are present in Uranium ore? I’ve seen the license maps of both granite quarries and Uranium mines, they overlap in many cases…. From reading Uranium mine reports, they are mining as low as 80 ppm Uranium ores these days, stating that 25 x background levels are particularly lucrative for mining. They mention 80 to 100 uR/hr granite being a cash cow, although they don’t specifically say what type of radiation, they mention Gamma Spectrometry which leads me to believe they are talking about Gamma only. Please correct me if I am wrong.
http://youtube.com/user/TCSRock78
If one is to believe their eyes, some of these granite slabs waiting to be sold for granite countertops, are way over that 80 to 100 uR/hr floor for economically Uranium mining. Would it not follow that these slabs contain “Uranium ore” in at least small quanities? Were you to see a slab that emitted over 100 uR/hr consistently throughout the majority of the slab, would you say that that slab contained Uranium ore?
Your last sentence, about the radiation resulting in very unusual colors and textures, and that the feldspar has become almost black. Is not the goal of new mines to bring to market those very same “very unusual colors and textures”? You mention of the black color being indicative of high levels of Uranium is exactly what we are finding in granite slabs in slab yards in our area. More on this issue a bit later.
Next:
“High localized readings of radioactivity in granite are the result of several possible geological processes. One is from the presence of sparsely scattered accessory minerals such as zircon, allanite, sphene and monazite that are intrinsic to granites. These minerals incorporate small to trace amounts of lanthanide and actinide elements into their lattices. Gradually, the uranium and thorium in these typically sparse minerals decay by various mechanisms and release tiny amounts of radon and thoron. Minerals that constitute uranium ore (mainly pitchblende, uraninite, torbernite) are exceedingly rare in commercial granites”
This site, http://en.wikipedia.org/wiki/Monazite
says that monazite contains Uranium as well as Lanthanide, but also Thorium and Cerium which also has many radioactive isotopes
http://en.wikipedia.org/wiki/Cerium
Allanite has been reported to have Thorium content and other radioactive elements present, indeed the a halo of radiation damage in the minerals immediately adjacent has been reported as you brought up on other minerals.
It seems that you might be parsing words here, saying that zircon, allanite, sphene and monazite contain only trace amounts of lanthanide and actinide, then bringing up their Uranium and Thorium content as an afterthought. Perhaps it is not coyness, but the scientist in you being specific, yet I find it less than reassuring. Could you not just say that they all contained Uranuim and Thorium and be done with it? And if they are currently mining granite at 80 ppm of Uranium, would it not be safe to say that some granites contain Uranium ore or that some Uranium ores are found in granite?
Next:
“In both these geological situations there is always the possibility for some localized concentration of the accessory minerals. In particular, the way some granites are formed involves the natural concentration of restite (residual) minerals. Where this occurs there could be localized elevated readings of radioactivity. Contamination from and/or partial assimilation of argillaceous country rock (such as mudstone and shale) by the intrusive granite as it forces its way to higher crustal levels can also lead to localized higher readings.”
Why not just agree with us that there are indeed hot spots in granite? I could care less how they got there, I just want them cut out.
Next:
“Uranium minerals can also form as a result of fluid activity within or associated with a granite body. It can happen during the formation of the granite, during emplacement of the granite or post-emplacement from external sources. High-level felsic granites may generate fluid activity that is able to scavenge uranium and thorium from the breakdown of some of the actinide-bearing accessory minerals and/or their hosts. Under certain conditions these fluids can permeate through the granite (mainly along grain boundaries) causing alteration of the feldspar to mostly kaolinitic clay and sericitic mica. The uranium and thorium can be adsorbed onto the clays and mica. As emphasized above, where such a geological process can be readily identified, the resulting granite type has become structurally weakened and is no longer a viable commodity for construction or use in the countertop industry. ”
I agree that the radioactivity can run in veins and we have found that the hottest spots are very weak, many have been repaired at the slab processing plant, resined so that the slab can be sold. One would not know these spots were epoxied in, they look just like the other black spots. One of the dangers of these hot spots is their fragility that you mentioned. Some consumers have remarked on “grainy” residue on new tops and even old tops that a thick sealing can stop, could well be that these tiny particles are indeed the weakened minerals you mentioned.
On that note, the practice of resining and mesh backing many stones that are otherwise too weak to process and transport. Certainly these processes that add plenty to the costs of production are used to bring to market stones that you say are ” structurally weakened and is no longer a viable commodity for construction or use in the countertop industry “. And add your comments on the unusual colors and textures, and BANG, Bob’s your uncle. Premium slabs for sale…
Would you not concede that resining and mesh backed stones would be indicative of a “structurally weakened” granite and that after resining and mesh backing, that stone can be brought to market profitably for the granite countertop industry?
Next you write:
“High levels of fluid can also result in some localized geological “oddities” such as pegmatite. The huge grainsize and spectacular textures are in high demand because of their rarity. Their formation can involve the concentration of rare elements which either become incorporated into the structures of other minerals or, where sufficient, can form large and exotic minerals. If the fluids have scavenged some lanthanide and actinide elements there is a likelihood of creating sparsely occurring minerals containing elevated concentrations that lead to spikes in the level of radioactivity. ”
Dr Hans, respectfully, you make our case that the higher cost granites are the most risky. And can we stop with the “lanthanide and actinide” and just use Uranium and Thorium? Incidently, how can you be so sure they are “sparse”? Are not most Uranium deposits leached from granite, as your mention of “high levels of fluid” seem to indicate? And again, the Pegmatites are in great demand for their uniqueness, thus the high prices.
Next:
“The fact that there is a localized high concentration of uranium sufficient to mine in proximity to a granite does not mean that the granite must also be high in uranium.”
Would you not agree that the proximity of a Uranium mine to a granite quarry does not mean that the granite does not have high levels of Uranium as well? We both know that they core drill the sites to map out the concentrations. Is it not feasible that a dyke of these same pegmatites that you said were in such high demand might well surface in the granite quarry?
Then:
“If you are concerned at all about radioactivity and radon in your home coming from your kitchen countertop think BLACK.”
I agree 100%, most of the black types of “granite” are low level.
Next:
“Because the majority of radiation emitted from felsic granites is from potassium (40K) and not from the uranium (238U) series as suggested by the physics researcher (commonly by a factor of 10) it follows that granites with an abundance of alkali feldspar are generally more radioactive and greater radon emitters than granites poor in this mineral. ”
I agree again that much of the radiation is coming from the Potassium (40K), but according to this site
http://en.wikipedia.org/wiki/Potassium#Isotopes
Potassium 40K decays by Beta decay, Positron emission, and electron capture, no where do I see any mention of Gamma being produced. So, if a scintillator is used to measure the radiation, and by design that scintillator can only measure Gamma not Beta, any Beta radiation is not counted any way. All the radiation is Gamma, is it not? How is it relevant that Potassium accounts for most of the radiation when we aren’t counting that type of radiation? This seems to be a red herring thrown in to confuse the readers, perhaps it is not….
Next:
“It must be emphasized that in most radon measurements the 220thoron contribution is generally neglected because it is more difficult to measure accurately with common instrumentation, because there is a difficulty in obtaining representative mean values due to as yet poorly understood short and long-term concentration fluctuations, and because of its shorter half-life (about 55 seconds). However, what has been established is that thoron is ubiquitous in our environment and typically contributes to about 25% of the total signal. In some places it may be present in much higher concentrations than radon. Because its presence affects the radon measurement it also affects the dose evaluation.
I agree that Thoron can interfere with Radon measurements, but due to it’s short 55 second half life, would you not agree that there is a very strong likely hood of breathing quantities of Thoron and having it decay inside your lungs while using a granite countertop? The half life doesn’t mean it is all gone at 55 seconds, only have of it is gone. At 110 seconds, 25% is still undecayed, at 165 seconds, 12.5 % is still undecayed, at 220 seconds 6.25% is still undecayed, and so on. I argue that the greatest risk of a granite countertop is using it, not the effect it has on the rest of the homes Radon levels. The Houston report validated this, the rest of the home was al low levels, but the kitchen had over 14 pCi/L of Radon present!
And since the Thoron and Radon is continually produced, there is a never ending supply of these gases for the occupants of the home to breath….
Would you not agree that standing over a countertop, or a child doing homework or coloring a color book is at more risk from breathing the Radon or Thoron than Dad in his easy chair in the living room? Just your personal opinion, as you are not a health physicist.
Next:
“Given these imposing collective factors how much reliance can be placed on the accuracy of domestic “radon” readings carried out by untrained people with $5-$10 radon meters whose activated films require mailing to a laboratory within a short time? The frenzy to purchase radon meters in Houston and other parts of the US as a result of the initial radio announcement is similar in a way to a clever and successful media stunt in Australia to ban the often deadly chemical dihydrogen monoxide. Dihydrogen monoxide can be highly dangerous in its natural form and is a common component of many dangerous toxins. It is responsible for thousands of deaths each year. ”
So, if the public can not depend on their fabricators, the wholesalers or the MIA to test their granite, are you suggesting that they just not test their tops? Those cheap Radon meters are usually sponsored by the state Radon office, so someone must have some faith in their accuracy, indeed those tests must meet EPA standards for accuracy. It sounds more like you are afraid of what the $5.00 meters might find.
Save the Dihydrogen monoxide, BS. Other stoners have used that one. Water…..
Then:
“• 30,000 atoms disintegrate every hour in our lungs from the air we breathe giving off mainly α and β particles”
You are referring to the usual Radon in the air we breath. Are you advocating we add more? I understand that a quart of air at 1 pCi/L will have 12,000 atom decays per hour. Your figure is much higher. Would you mind if I use that figure and quote you on it? Since you are not a health physicist, you might not be up to date on the latest info, but would you comment on the bystander effect of a single Alpha or Beta particle on lung tissue?
“Also of relevance to this debate of naturally occurring radiation is the fact that radiological/epidemiological effects that can be directly attributable to continuous low level radiation are poorly understood because of the infinite other possible interactions in our complex environment and the intrinsic chemical and physical properties of the numerous relative daughter products of the 238U, 235U, and 232Th decay chains. ”
Are you saying that the ALARA doctrine, As Low As Reasonably Achievable, is to be dismissed as sound advice? Did not BEIR and the ICRP endorse this doctrine? Since we can’t be 100% certain, can you explain why we would err on the side of danger, not safety? Would it not be better to purchase a lower level stone than a higher level stone? Doesn’t that require testing of every slab?
Next:
“It may be of interest to potential consumers of stone that certain varieties of engineered stone (quartz surfaces) consist of a framework of crushed granite particles. Boasting around 93% (by weight) of framework particles, petrographic analysis revealed the presence of the usual radioactive accessories, such as zircon, allanite, sphene and apatite, as well secondary clays and micas. If any studies are to be undertaken they should also include the altered and weathered brownish, granite-based synthetic products which would be expected to yield similar results to most common granites. Any testing authority must be aware that it is important to avoid being presented with only the relatively “clean” quartz pebble based engineered stone because of the inherently low level of radioactivity in quartz. ”
I agree 100% that quartz should be tested as well. In fact, I sent both Staron and Hanstone quartz samples, brand new expensive sample boxes, to Dr. Llope for that purpose. I can tell you that it is a fools errand but to head off those like yourself that will cast suspicions on Quartz materials to take the heat off your product. I have measured quarz, entire lines of three companies so far. At background levels or slightly above, maybe 1 to 2 uR/hr, so after you subtract the background radiation from the test result, zero to 1 or 2 uR/hr radiation. A factor of 4 times less radiation than the quietest granite we have found to date. I tested an entire warehouse of Hanstone. Not a single beep, not a single instance of radiation over background. In fact, there was less radiation present than in the Importers offices.
Attempting to cast suspicion on quartz is desperate behavior, completely out of tune with the rest of your post. I would ask that you retract that attack unless you have proof to back your suspicions. If though, you have proof of engineered stones that do contain radioactivity, I would also ask to be given their names so I can procure samples and send them for testing.
All the bad products must be taken off the market no matter who sells them…..
Oh, and this one….:
“The synthetic surfaces industry has had a history of advertising misinformation verbally and in their written presentations regarding their own products and their natural stone competitors. An article written in 2005 entitled “Some aspects of engineered stone that are not usually advertised” could not get published in its long version by stone magazines because of the ostensibly potential litigious effects but, more honestly, the potential damage to the hip pocket in terms of advertising. The link below might be of interest. Some aspects might now be out of date because of new (Asian) producers and the inability to obtain samples from other suppliers – especially from the US. A condensed version of the article was released by the MIA as a newsletter. Although it faithfully portrayed the gist of the paper most of the details were omitted.”
Pray tell, Dr. Hans, who wrote that White Paper?
In that article, which you say faithfully portrayed the gist, there are several problems. For starters, you mix engineered stone with Quartz, while not pointing out that a quartz based product has only quartz as the filler, not the marble that you rightly claim degrades the marble based engineered stones performance. Will you admit that lumping the two while knowing that quartz specifically does not have marble content is misleading? Seems quite a slip for such a smart guy. Then again, if Marble is so bad, why did you help The Marble Institute with that white paper?
Next you claim in that paper that “engineered stone” has radioactivity. Again, please separate Quartz from marble based engineered stone and provide proof that the marble based products contain radioactivity. Were you to do so, expect the level you show to be the new level at which granite should be rejected as being too high.
Your next claim in that white paper is that quartz claims 1610 degrees heat resistance. Clever, or maybe not. It is obvious that you are referring to the quartz content, not the resin content.
Here is the Silestone MSDS sheet with no mention of the info you are claiming.
http://www.sterling-mfg.com/pdf/SilestoneMSDS.pdf
All quartz products are sold as not heat proof, but heat resistant. All carry warnings not to place hot pots directly on the surface. Granite on the other hand, claims heat resistance without saying that thermal expansion can crack the granite, if it doesn’t crack from the cabinets settling. Completely unacceptable to bring up these red herrings while hiding your own products issues.
Notice the only hazardous substance listed? Quartz dust for its silica content. You saying that granite has none?
And it just gets better, don’t it?
“Another aspect that might be of interest is the movement in about 1985 in Australia to undertake studies of radiation levels and associated radon/thoron gas emissions from both domestic and imported stone. This follows the reported monitoring of stone for these products in Sweden and Canada. The movement fell through because of funding difficulties, because it was deemed unimportant in terms of health issues, and because there was a perception that it might adversely affect a small and fragile, domestic granite industry. ”
So, it seems that the funds couldn’t be raised and there was a perception that testing might adversely affect the granite industry… Now we are getting somewhere.
Tell me this, Dr. Hans, are we to sacrifice safety for the financial interests of the stone industry? Since twenty years have passed, has not the industry had time to test products and bring only safe products to the market? Since we now know that high level radioactive granite is being sold, doesn’t that knock the third leg off that 1985 argument?
And:
“A final note is necessary on the rather ludicrous notion that regular maintenance of granite kitchen countertops (including sealing the surface annually) will in some way influence the radiation flux and radon emissions from that surface.”
Are you going to address that issue? One sealer company has approached us for help in testing just that, does sealing lock in the Alpha if nothing else. You position please?
And then:
“As for the ill-conceived and impractical idea on the testing of every slab, tile and block of stone that enters into the US and is produced in the US clearly the Rice University particle physicist has little knowledge of the diverse stone industry. All slate would require testing, all sandstone products (because of the possibility of thin beds of natural heavy mineral concentrations), all sand used for construction, the gypsum used to make plaster for walls and ceilings, and every aggregate source that uses its product to make concrete. In almost all dwellings these other construction products far exceed the amount of granite that is used.”
Is your argument that because other products might be a problem, that your product shouldn’t be tested? How many slate countertops are used? Sandstone? Is sand normally present inside homes? Is the Gypsum drywall normally coated with heavy paper and then coats of paint? Will these not block Alpha and most Beta? Aggregate in concrete, well that makes sense for a concrete countertop, but is the floor not covered in some manner with material that will block Alpha and most Beta? Even stained concrete floors have a coating….
In all dwellings, these other construction products aren’t used in the raw form, sitting two feet away from your nose while being used, nor is the mass of a slate backsplash near the mass of a granite countertop.
And finally:
“A commonly encountered and quite serious problem these days is the function of the testing laboratory and laboratory personnel not only in the testing but also in the interpretation of the data. Laboratories (and that includes many university departments where instrumental testing is carried out) employ technicians who are trained in most aspects of instrumentation and in the conduction of certain tests. They are generally not trained in the understanding of the materials they are testing nor in the interpretation or significance of the results. Instrumentation specialists should limit themselves to the understanding of the instruments that they are using for testing and engage a suitably qualified scientist to assess and interpret the results, even when the testing appears to be straight-forward.”
Using your own arguments above, would you not also admit that you personally do not have the qualifications to judge the health risks of the radiation in high level granites? Would it not be better to rely on EPA standards, ICRP standards, than your own guesses? Should not Geo chemists also be limited to their fields of expertise?
I appreciate your joining the fray. I would also think it would be a good idea to tell the readers of any paid work you have done for the MIA in the past, any white papers you might have written, and whether or not you are currently working on projects for the natural stone industry.
Oh, and about that white paper that got rejected by Surface Fabrication, who did you say wrote that article?
Respectfully,
Al Gerhart

In the search for more information, the Uranium mining industry has been a source of excellent reports and science. Unlike the stone industry, the Uranium industry is very forthcoming on locations of mines, environmental aspects, and health aspects of low level radiation. The knowledge given in their reports also helps us understand how to correlate parts per million (ppm) with uR/hr levels.

This report on a Canadian Uranium mine site

shows some interesting figures on the ppm content of Uranium ore. It looks like between 3 and 4 ppm of Uranium in granite is about the same as background radiation, and once a granite is found with 25 times background level, that indicates a economically viable Uranium mining site. So between 75 and 100 ppm can be mined profitably. If background radiation is 3 or 4, that puts the granite at that site between 75 and 100 uR/hr.

Plenty of granites have already been found above 75 uR/hr Gamma, assuming that that is all they are measuring. If they are using Alpha and Beta as well, that probably doubles or triples the granites that would have enough Uranium content to economically mine.

Another measurement they used was Counts Per Minute, CPM. From 500 to 4,000 cpm were found through out the prospective mining site. Up to 65,000 hot spots were also recorded, but apparently 500 to 4,000 cpm is high enough to warrant Uranium mining.

Again, many granites have this much radiation. Lots of common granite such as Uba Tuba will average 360 cpm, making them too low for economical mining, but they have close to the same health risks of raw Uranium ore. And they could be sitting in your house in large masses.

Many times, a study on suspected carcinogens is made difficult by other factors that may lead to cancer.

This ten year long study on Uranium miners in Namibia, got around the problem because of its remote location, far from poor quality air or industrial plants that might pollute the local area. The study found higher rates of cancer among miners than the general population.

The idea was to see if low level radiation from Uranium mining caused radiation damage leading to cancer. Seventy five non smoking, HIV negative miners were studied by blood work and urine analysis for Uranium elimination. The results were compared to a cohort of 31 men with no Uranium mining experience. The average exposure was 1.8 mSv/yr, the highest was 5 mSv/yr, well within the ICRP dose limit recommendations.

The Uranium miners excreted six times the Uranium than the non miners, and had a significantly lower Testosterone along with more chromosome aberrations. The most remarkable finding was cells with multiple chromosome aberrations, so called “rogue” cells were found in the miners. These rogue cells were previously found only after high radiation exposure in Hiroshima or Chernobyl survivors.

The study concluded that low level radiation was responsible for genetic damage and malignant transformation, as well as lower hormone levels and damage to other body systems.

Coupled with the known measurements of granite countertop materials, this study would point to the same health issues that granite fabricators and homeowners with high radiation granite countertops would face.

In the coming days, we will show more Uranium mine info, and the granite slab quarries that are very near some of the larger mines.

On the 6th of June, the EPA changed their long standing position that granite countertops did not present a health risk to homeowners. The stone industry had used the EPA’s stance to bolster their claims that granite countertops presented no risk.

What brought the change was the Houston TV report. A copy of the report was requested by the EPA the day after the report ran, then after a new question was asked about Radon and granite countertops, the EPA replied that they were researching a new position on the matter.

Today, we received a reply to the question. The EPA now states that there is some evidence of granites with high enough Uranium to emit Radon. They recomend that consumers with granite countertop test the air in the home first and mitigate if the result is 4 pCi/L or more.

EPA’s new position on Radon and granite

Seems the facts have impressed even the government on this issue. Wonder if the stone industry will eventually come around?

June 4th, 2008
The short answer is yes, you should be concerned. Three facts stand out.

The scientific standard for radiation protection is ALARA, As Low As Reasonably Achievable.

Almost all granite has some level of radiation.

Radiation can cause health problems and disease.

But, the real answer is not black and white. In fact, what you will wind up doing is finding out the risk factor for your choice of granite, then deciding if it is worth the risk. Could be a tiny, tiny, risk or could be a huge risk.

For many years, the facts about radiation and granite countertops were successfully suppressed by the Marble Institute of America (MIA) which is the main stone lobby association. One can google the terms and find website after website saying that this is a myth started by laminate or solid surface manufacturers, but get past page one on the Google search, and the scientific studies on granite start showing up. Also, competing product associations, like our’s, have started to gather the data so it is easily found by consumers.

So there are really three camps, those that claim the granite/radiation issue is a myth, those that now admit the issues but claim all granite sold are low level, and those like this site that show that there are high radioactive level granites being sold to consumers. Who to believe?

The facts, proven by scientific studies, reports of hot granite tops being removed, and by informal testing on actual granite slabs, show that there are some granites being sold that emit seriously high radiation. As this blog site develops, plenty of proof will be presented, actual data logs from testing granites, pictures of high level readings, even videos of the entire process. Scientific studies will be linked to, as well as other forums with postings by experts in the field on the issues.

For now though, what should a consumer do if they want a granite countertop? Seven main points to consider in deciding on the level of radiation you will accept as worth the risk.

A. Do your homework. Spend some time online getting all sides of the story. Not likely that someone selling only granite countertops will be credible, but find out what they have to say. Better to find company web sites like mine, that offer all types of countertops. We just want to sell you a top, doesn’t matter which you pick in the end.

B. Figure out how much time you usually spend in the kitchen. A homemaker with a large family that is an avid cook will spend a lot of time in a kitchen, but a single person with a demanding job may not use a kitchen much at all. Time, distance, and mass are important factors in radiation exposure, so a seldom used kitchen can use a hotter granite. A smaller kitchen might justify choosing a slightly hotter granite.

C. Consider your family health history. If cancer runs in your family, as it does in mine, you will want to consider a lower level granite. Other diseases have been linked to radioactivity as well, so find out what is an issue in your family.

D. Consider any exposure you get from other sources. A nuclear plant worker will likely have a pretty low exposure history, strangely enough, but a medical researcher or X ray tech might have a higher yearly exposure. Those living at higher elevations receive more cosmic radiation. Those in high Radon areas receive that exposure.

E. Find a countertop fabricator that takes the issue seriously. They will have the knowledge and equipment to test your slab prior to purchase.

F. Find out if the material you are interested has been tested. Some like Absolute Black seem to be safe, and tend to be very uniform levels, few if any hot spots. Others can be low level on one end, very hot on the other end. Some have small hot spots that can be cut out if the fabricator knows to test to find them.

G. Have YOUR slab tested prior to purchase, don’t put down a cent till this is done, and insist on seeing the process. It takes but a couple of minutes for a properly equipped fabricator to do a simple survey on the entire slab. The equipment is simple, relatively low cost, and requires no training to understand the reading.

Understanding the risk from that reading does require an expert, who would have to know, exactly what radioactive elements are present, how much, how long, and how close. General rules of thumb for radiation risk are available, as well as exposure limits, so a general idea can be easily determined. Will the answer be exact? No, but it doesn’t need to be. We will confine our work to sorting high from low levels, leaving exact measurements to the Nuclear Physicist and Health Physicists.

As this site develops, we will address everything one needs to know and do to find a safe granite countertop.

Thanks for reading, comments always valued,

AL Gerhart

June 5th, 2008
Think of the earths crust as a big mixer, or like a bunch of big mixers side by side. Some mixers will run longer, so the mixture might be pretty uniform. Other mixers might get bumped on once or twice, leaving little uniformity in the mix. Some mixers might have new ingredients added right before the end, resulting in veins or pockets of materials.
Granite can be uniform, but usually it isn’t. Some of the more uniform types are Absolute Black or Uba Tuba. These tend to test in a narrow range. But even within a single quarry, Uba Tuba will vary widely in color and quality, from quarry to quarry, the difference is even more pronounced.
Some granites are conglomerations, lots of movement and colors happening. These types of granite are the most unpredictable. I have seen slabs that test 15uR/hr on one spot, test 150 uR/hr on wide portions of the slab, then test 800 uR/hr on hot spots.
Currently, only a four or five hundred samples or so have been tested and reported worldwide. Some of the more comprehensive tests tested 80 stones or more, others tested a dozen or less. To my knowledge, no one but the SSA has ever tested multiple samples of the same type granite to find a range the stone usually tests in. So this science is in its infancy, too soon to say that any particular stone will always test safe.
To complicate things, the granite industry tends to be very fragmented. Sometimes a farmer opens a quarry, sells blocks to a processor that slices and polishes the slabs, then an importer buys the slabs and imports them, reselling to a slab yard or fabricator. In china, a licensed trader has to export the slabs, adding a another layer to the supply chain.
The importers, slab yards, and even the fabricators don’t want people shopping around on price, so they tend to use different names for the same stone. Called the name game, this can be a problem to consumers. You find a nice stone, but can find it in only one slab yard. Sometimes you can’t find any info at all on the Internet on your choice of stone. This becomes important for testing, who knows the real name of the stone so it can be tracked back to the quarry?
Plus, is there a chance that once a stone is know to test high radiation, nothing keeps the sellers from just changing the name so the stone can be sold. Our granite suppliers tell us that the stone industry is one of the most corrupt industry’s around. The going rate for bribing an inspector/agent is 4% of the value of the slab, so a $10 bribe will get a substandard slab left on the shipment instead of being rejected.
So, to be certain, we recommend that all slabs be tested prior to purchase. Our shop insists on this. It just makes sense given the expense of the projects.