[ RadSafe ] Radioactivity in Granite Countertops

[Dan McCarn]

Dear Stewart:

There are virtually no "granites" that do not contain measurable, usually
elevated and sometimes and sometimes near ore-grade quantities of uranium,
thorium and daughters. I imagine that the dimension stone industry has
scoured the marketplace for quarries with granites having very low
background levels of radiation.

However, the term "granite" as used by the dimension stone industry means
all dimension stone including marbles, true granites, pegmatites and mafic
rocks (peridotite, labradorite, etc.). So there are many "granites" that
contain low levels of radiation, but most are not true "granites" as
defined by the Colorado School of Mines Rock Classification Scheme
- "CLASSIFICATION OF ROCKS", Quarterly of the Colorado School of Mines,
Volume 50, Number 1, January 1955, by Russell B. Travis.

There are granites that contain low levels of uranium, but there are also
anatectic granites (alaskites) that contain in excess of 100 mg/kg U such
as in Namibia.  Pegmatites have the potential of containing even
higher quantities of uranium and there are some Brazilian "granites" that
are quite hot containing nearly ore-grade concentrations. Some of the
anatectic granites from Namibia have found there way into the marketplace
and are quite "hot".

There are artificial granites that are virtually devoid of K, U Th &
progeny.  I wrote an "Opinion" for one of these artificial "granites" after
receiving analytical data from a lab certifying that the artificial stone
was below normal background levels of radiation.

I also wrote a response for another sample for the Solid Surface Alliance
some years back (2008) that is still available on the web:

http://solidsurfacealliance.org/blog/category/granite-radiation/

In that case, the "granite" contained about 0.25% U and was probably a hot
spot from a pegmatite or vien. I wrote at that time, "When granitic
batholiths are intruded, the last remaining watery portions of the magma,
having gone through differential precipitation (Bowen Reaction Series), is
enriched in uranium and sometimes other metals e.g. tantalum, gold. These
quartz-rich remainders can form intra-batholithic intrusions or
peri-batholithic intrusions enriched in uranium. "

Best,

Dan ii

Dan W McCarn, Geologist
108 Sherwood Blvd
Los Alamos, NM 87544-3425
+1-505-672-2014 (Home – New Mexico)
+1-505-670-8123 (Mobile - New Mexico)
HotGreenChile at gmail.com (Private email) HotGreenChile at gmail dot com




On Mon, Feb 27, 2012 at 11:39 AM, Stewart Farber <SAFarber at optonline.net>wrote:

> Does anyone know if there some types of granite that contain NO enhanced
> levels of natural radioactivity? This has never been my experience, but I'm
> no geologist.
>
>
>
> I've done studies with high-pressure ionization chambers in many places
> showing clearly elevated levels of radioactivity contained in granite in
> construction throughout the Northeastern US as indicated by elevated gamma
> dose rates of 20 micro-R/hr [200 nSv/hr] or more  [ in close proximity to
> granite walls -approx. 1 foot distant] vs. typical background dose rates
>  of
> about 8 micro-R/hr [ 80 nSv/hr] for the area.
>
>
>
> Every HPIC measurement near granite I've made around Boston [ at the
> Christian Science Church, South Station, Bunker Hill Monument, steps of the
> MA Statehouse, granite Colonial era wharf buildings]  or all around
> Westerly, RI [a town where almost every building is made of granite], or in
> NH or Maine, or  the Harrisburg, PA Capitol granite steps,  has shown about
> a doubling of background dose rate measured with a HPIC a  foot  or so from
> the granite used in construction.
>
>
>
> Another interesting measurement was of a doubling of background dose rate
> near a large piece of Aswan red granite from Egypt which was used to make a
> sarcophagus for a princess many thousands of  years ago. This ancient
> granite ceremonial Egyptian coffin is currently displayed in front of the
> Boston, MA Museum of Science.
>
>
>
> All  granite mentioned  above would show greatly elevated count rates when
> measured on contact with a standard pancake GM like an Ludlum 44-9 or
> HP-360.
>
>
>
> However, a friend has recently installed granite countertops which shows
> background rad levels on contact. So has my friend purchased "real" granite
> with all the  natural radioactivity it "should" contain or has she been
> cheated of her little bit of residual elevated U-238, Th-232, and K-40
> radioactivity from the Big Bang?
>
>
>
> Thoughts?
>
>
>
>
>
> Stewart Farber
>
>
>
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