[ RadSafe ] Radioactivity in Granite Countertops

Mon Feb 27 15:11:30 CST 2012

Hi Dan,

Thanks very much for your information.

The "granite" counters my friend purchased, while attractive, do not have
the small grained inclusions that I associate with the granite I've seen
used in construction of buildings, building facing, steps, tombstones, etc.
When I could not get an elevated count rate, even with a thin-window pancake
GM on contact with the "granite" counters in question,  I became suspicious
that she was supplied something other than  "granite". To my mind, if a
retail outlet advertises their product as "granite" and charges a premium
rate for it per ft^2 [or m^2 or whatever metric unit some want used] the
buyer has paid for something they did not get. 

True granite to me has certain specific properties which would not be seen
in marble, or other types of dimension stone you mention. Your reference to:
the Colorado School of Mines Rock Classification Scheme - "CLASSIFICATION OF
ROCKS" definition as to what is true "granite" is interesting.  If a stone
does not meet the classification of "true granite", has a buyer paid for and
not received a stone counter which has properties as to durability,
hardness,  etc. that are not up to what it should have been?

Stewart Farber

Stewart Farber, MSPH

Farber Medical Solutions, LLC

Bridgeport, CT 06604

SAFarber at optonline.net

203-441-8433

From: Dan McCarn [mailto:hotgreenchile at gmail.com] 
Sent: Monday, February 27, 2012 3:31 PM
To: safarber at optonline.net; The International Radiation Protection (Health
Physics) Mailing List
Subject: Re: [ RadSafe ] Radioactivity in Granite Countertops

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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