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TITLE: Quartz

[Photo: Different Forms of Quartz]

Large Crystals
Quartz is all around us. It is the major component of beach sand and many rocks. Under the right conditions, quartz can form large, nearly perfect crystals—sometimes with vivid colors that transform an everyday mineral into an exquisite jewel.

[Photo: Different Forms of Quartz]

Tiny Crystals
You need a microscope to see the individual crystals in these specimens. But you can see the patterns, colors, and textures that make fine-grained quartz popular as an ornamental stone. There are two main groups of fine-grained quartz. In chert, tiny crystals interlock to create a grainy texture. In chalcedony, fibrous crystals intergrow, yielding an array of patterns. Each group has many subvarieties, defined by their colors and patterns. Agate is a concentrically banded variety of chalcedony made up of tiny fibrous crystals. Agate forms in cavities left by gas bubbles in cooling lava. Silica-rich groundwater builds layers of crystals on the cavity walls.

[Photo: Different Forms of Quartz]

Useful Crystals
Quartz sand is the most important raw material for the glass and ceramics industries. It is also an additive in cement and mortar and a source of silicon for computer chips. Crystals of synthetic quartz, as seen in the image to the right, made largely from sand, are used in lenses and watches. To keep time, watches rely on quartz's piezoelectricity: Quartz crystals vibrate in response to an electric current at a specific frequency, depending on the thickness of the crystal.

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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits