Brazilian Quartz Crystal at Rock and Mineral Show

July 14, 2008

071408

Provided by: Thomas McGuire, Textbook Author/Educator
Summary Author and Editor: Thomas McGuire

Mineral crystals grow under a variety of conditions. Slow cooling of magma (melted rock) deep within the Earth generally leads to a rock such as granite with visible crystals of feldspar, quartz, mica, amphibole and other minerals. Water in the magma can even facilitate pegmatite formation. Pegmatite is an igneous rock composed of mineral crystals generally with a diameter of several centimeters which, on rare occasions, can be meters.

The individual crystals or crystal groups that people generally collect or purchase have more often grown in openings through which superheated water circulates. Water is a remarkable solvent. Most minerals are water soluble, even if only in minute concentrations. Thus water can slowly transport and deposit layer upon layer of molecules to build mineral crystals of impressive size. In fact, the geometric forms of crystals are among the most readily observed evidence that matter is composed of discrete molecules and atoms.

This giant crystal of quartz was displayed at the 2008 Tucson, Arizona, Rock and Mineral Show, an annual event in early February. In addition to the convention center displays, vendors from all over the world show and sell geological specimens both wholesale and retail at several dozen satellite shows throughout the city.

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