Smoke quartz
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Smoke quartz

by Konstantinos Kourtidis, Demokritus University of Thrace, Xanthi, Greece

The Smoke quartz chemical formula is SiO2. The crystal system is trigonal. Smoke quartz orginates from colorless quartz, that changes colour because of exposure to radioactivity. The one in the photo, found near Little Rock, has been artificially exposed.