Irradiated Quartz Crystal (Smoky Quartz)
The photograph shows two quartz crystals each of which is approximately
1.5" across. The difference between the two is that the crystal on the
right has been irradiated with cobalt-60 gamma rays to turn it gray.
Gray-colored quartz is referred to as "Smoky Quartz." The
color of the smoky quartz found in nature is due to its exposure to
gamma rays from naturally occurring radionuclides such as potassium-40 and
members of the uranium and thorium decay series. For the quartz to turn
gray, it must contain trace amounts of aluminum.
Radiation, Heat -- Improve Natures Gems. Lithosphere, June 1993. http://fgms.home.att.net/impgems.htm
Ashbaugh, C.E. Radioactive and Radiation Treated Gemstones. Radioactivity and Radiochemistry, Vol. 2(1): 42-56.
Copyright 1999, Oak Ridge Associated Universities