Finding high radiation readings from some granite slabs intended for use as kitchen countertops led me to find out why we were finding high levels of radiation from some granites & not others.
We purchased radiation detection equipment to verify the existence of radiation in granite.
Our first visit to a slab yard gave us 1 granite that read quite high. It was what we expected though as we had heard that Bordeaux was a culprit behind high radon readings in homes. The Bordeaux that we found generally read 60 uR/hr. (micro rad per hour) with our scintillator which measures gamma radiation. In one spot it read 100 uR/hr.
We became concerned with this reading and so we contacted our state DEQ & he told us to be very careful when fabricating this material & to dispose of the scraps only in a hazardous waste facility.
We decided to move on & test other slab yards to see what else we could find. As we were expecting only Bordeaux to emit high readings we were surprised & shocked by our next find. We came upon Niagara Gold & our scintillator was going nuts just upon walking up to it. We scanned it with our scintillator & found one spot reading over 400 uR/hr. The whole slab was generally 150 - 200 uR/hr. The label on the slab said "Made in Italy".
I decided to find more information on where the slab came from & when I tried to google it I only came up with Niagara Gold from Namibia.
It was upon this discovery that I decided to do more digging & find the exact location of the quarry. I found references to a US based company & their investment in a Stone Africa quarry in Namibia & then I found out that Namibia is the 5th largest producer of Uranium in the world.
So we told our supplier of what we were finding & he invited us down to his warehouse. We found a slab of Four Seasons granite that had a hot spot measuring over 800 uR/hr. The vast majority of the granite in his warehouse did not produce levels to be concerned with, with the exception of Bordeaux & Four Seasons.
While not all granites are going to emit high levels of radiation, some are.
A granite quarry's proximity to a uranium mine is not always an indicator that it will produce high levels of radiation. We were made aware of a granite called Shivakasi that elevated a home's radon level to 14 picocuries. Sivakasi, Tamil Nadu state, India is not located near a uranium mine but according to the IAEA is in a region of high radioactivity due to Monasite sands.
So the lesson here is do some extensive research on the granite you intend to buy. Find out the country of orgin, (not the country where its produced but where it is quarried) & find out if there are any uranium mines nearby.
If you have Shivakasi, Bordeaux, Four Seasons, or any of the granites from Namibia get it tested for radiation & radon. So far these are the stones we have discovered to give off high radiation readings. There may be more.
If you are concerned you might just petition the MIA or congress to institute testing & labeling for granite.
Here are my links for more information:
Namibian licenses for nuclear fuel exploration (notice the overlap with the dimensional stone licences)
The management of Stone Africa apparently does not treat their workers very well. Would you want your stone coming from such a place?