Pegmatite

Physical Properties

Hardness: 6-7 (Mohs scale); Color: Variegated with pink, white, gray, and black splotches; Luster: Vitreous to pearly; Crystal structure: Very coarse-grained phaneritic; Cleavage: Good in feldspar crystals; Specific gravity: 2.6-2.8

Formation & Geological History

Formed during the final stages of a magma's crystallization, usually in water-rich environments that allow for the growth of exceptionally large crystals. This specimen appears to contain K-feldspar, quartz, and possibly some dark mica or tourmaline.

Uses & Applications

Sources of rare elements (lithium, tantalum), high-quality feldspar for ceramics, industrial quartz, and occasionally gemstones like tourmaline or beryl.

Geological Facts

Pegmatite crystals can grow to over 10 meters in length! They are known as the 'trash cans' of the geological world because they concentrate rare elements that don't fit easily into other mineral structures.

Field Identification & Locations

Identify by the exceptionally large, interlocking crystal grains of quartz and feldspar. Commonly found in mountainous regions or stable continental interiors (cratons) near large granite intrusions.

Identified on: 4/25/2026

Mode: Standard