San Diego Natural History Museum--Your Nature ConnectionSDNHM Field Guide
[Amethyst geode.  Collection of the San Diego Natural History Museum.]


Quartz is thought to have come from the German miner's language of the Middle Ages, but the original meaning is not known.

Description and Occurrence

Quartz is one of the most common minerals on Earth. The crystal forms as a six-sided prism with pointed ends. The ends look like six-sided pyramids. The sides of the crystal are marked with crosswise striations (ridges). It occurs in all geological environments, and makes up most of the dust in air.

Quartz comes in a wide range of colors. It's usually white and colorless, but is also transparent (rock crystal), purple (amethyst), pink (rose quartz), clear yellow (citrine), cloudy-white (milky quartz), and pale brown to black (smoky quartz). The more attractive colors are used as semi-precious gemstones. Amethyst and citrine are the most highly valued forms.

Most quartz crystals are not used as gemstones, but as raw materials in industry. It's used in glass, ceramics, paints, and abrasives. Quartz crystals are piezoelectric, and are used in watches, radios, oscillators, and wave stabilizers.

Quartz can be found anywhere on Earth. Fine specimens of rose quartz can be found in the pegmatite mining districts of San Diego County.

Field Notes: Quartz can be identified by its six-sided, prism-like shape and hardness.

Physical Properties

Color Streak Transparency Luster Hardness Cleavage Fracture Specific gravity Crystal form
colorless, various colors white transparent to opaque vitreous 7 none conchoidal 2.65 hexagonal

Photo: Amethyst geode. Collection of the San Diego Natural History Museum
Photo credit: Linda West

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