Sunday, July 21, 2013

Blue Apatites from Ipirá

I have heard, not long ago, that the blue Apatites from Ipirá, in Brazil, were radioactive.
I know that Apatites can be a little radioactive due to impurities of Th and U, so I decided to investigate a little further, since it is one of my favorite Apatites. 
I learned  that they have inclusions of Thorium and had a couple pieces tested here and yes,
they turned out to be radioactive indeed.
But how radioactive?
I contacted John Rakovan, a mineralogy professor in Ohio, that has an extensive knowledge about Apatites. And he kindly checked a couple pieces for me.
He used a nuclear radiation meter that detects alpha, beta, gamma and X-rays (but does not distinguish among them). 
At a distance of 1 cm he recorded 0.113 mrem/hour from the Apatite.
As a comparison, the background reading in his lab is 0.007 mrem/hour. 
A granite pegmatite sample of the same size from Moat Mountain, New Hampshire is 0.017 mrem/hour and a 1 cm specimen of Autunite gives off 6.624 mrem/hour.
"Given the US standards I would say that an average adult occasionally wearing an Ipirá would have no statistical increase in risk of cancer due to the radiation dosage. Even at a doubling of the average background dosage (aprox. 800 mrem/year) by wearing it all day, every day. The dosage is far below the US allowable dosage for radiation workers (5000 mrem/year). Allowable dosages are based on risk probabilities. If one has an understanding of radiation and radiation safety this is just fine, but for someone who does not understand, then there is likely to be fear from hearing that a gemstone is radioactive."
A nice site to read about radiation is the one at MIT


  1. Is it known what the cause of the colour is? Is it trace amounts of thorium? Where blue apatite occurs near Bancroft, Ontario, Canada, (Faraday Hill occurrence), it is in massive orange calcite associated with uraninite and minor molybdenite. When it occurs near Verona, Ontario (Canoe Lake roadcut and Lacey Phlogopite Mine), it is found in massive pink calcite with abundant phlogopite mica, and minor amounts of skarn minerals such as clinopyroxene and feldspar, but I observed no evidence of radioactive minerals.
    In the Bancroft area, just about any mineral that can accept radioactive elements (U & Th) into its structure does. Zircons, allanites and pyrochlores all carry abundant radioactives. I will look to have my apatites carefully tested, but until now they have all been considered free of radioactivity. Apatites tested very recently at a mineral show in London, Ontario showed that the Ipira blue apatites had very slightly greater than background radioactivity. Green apatites from Bancroft, (the most common colour), showed none, and one red coloured apatite from Lake Clear, Renfrew County, Ontario showed about seven times background. This area deserves more investigation.
    Chris Fouts, Bancroft, Ontario