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Quartz

The Rock-Forming Minerals

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Quartz (SiO2) is a silicate mineral and the most common mineral of the continental crust. Learn more about it in the Quartz Picture Gallery. (more below)
The continents' top mineral
Photo (c) 2009 Andrew Alden, licensed to About.com (fair use policy)
Quartz occurs as clear or cloudy crystals in a range of colors. It's also found as massive veins in igneous and metamorphic rocks. Quartz is the standard mineral for hardness 7 in the Mohs hardness scale.

This double-ended crystal is known as a Herkimer diamond, after its occurrence in a limestone in Herkimer County, New York. That's where I dug up this specimen. Once you're familiar with quartz, it's easy to recognize in many different settings.

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