Pegmatite

Physical Properties

Hardness (Mohs scale): 6-7; Color: White, cream, tan, or pink with glassy quartz; Luster: Vitreous to pearly; Crystal structure: Very large, interlocking crystals of feldspar and quartz; Cleavage: Good in feldspar grains; Specific gravity: 2.5-2.7

Formation & Geological History

Formed during the final stages of a magma's crystallization when high water content allows for rapid ion migration, resulting in exceptionally large crystals. Found in plutons and intrusive veins.

Uses & Applications

Used as a source for rare earth elements, gemstone mining (such as tourmaline or beryl), and as industrial quartz and feldspar for glass and ceramics.

Geological Facts

Pegmatite is known for containing crystals that can reach several meters in size. It is a 'giant' version of granite and often contains high concentrations of rare minerals not found in other rock types.

Field Identification & Locations

Identify by the exceptionally large crystal size (over 1 cm) compared to surrounding granite. Often found in dike formations. Collectors look for pockets of clear crystals or rare mineral inclusions.

Identified on: 5/1/2026

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