Cinnabar
(c) 2005 Andrew Alden, licensed to About.com, Inc. (fair use policy)
Cinnabar, mercury sulfide (HgS), is the principal ore of mercury. It is very dense, 8.1 times as dense as water, has a distinctive red streak and has hardness 2.5, barely scratchable by the fingernail. There are very few minerals that might be confused with cinnabar, but realgar is softer and cuprite is harder.
Cinnabar is deposited near the Earth's surface from hot solutions that have risen from bodies of magma far below. This crystalline crust, about 3 centimeters long, comes from Lake County, California, a volcanic area where mercury was mined until recently. Learn more about the geology of mercury here.
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