ALAN SIRULNIKOFF / SCIENCE PHOTO LIBRARY ALAN SIRULNIKOFF / SCIENCE PHOTO LIBRARY
Quartzite rocks. Quartzite is a metamorphic rock whose colour ranges from white (pure quartz) to black. It is formed by the metamorphism of a pure sandstone, the original quartz (silicon dioxide) grains being recrystallized and interlocking. The grey type seen here occurs due to minerals dispersed as tiny grains throughout the quartzite. Photographed in British Columbia, Canada.
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