Granitic Pegmatite

Physical Properties

Hardness: 6-7 (Mohs); Color: Yellowish-tan, brownish-orange, mottled with black and gray mineral grains; Luster: Vitreous to dull; Crystal structure: Phaneritic (very large crystals); Cleavage: Perfect in feldspars.

Formation & Geological History

Formed through the slow crystallization of magma at depth, often in the late stage of a granitic intrusion where high water content allows for the growth of large crystals. Found in shield areas and mountain belts across various geological eras.

Uses & Applications

Used as a major source of rare earth elements, industrial minerals like quartz and feldspar, and occasionally gemstones like tourmaline or garnet.

Geological Facts

Pegmatites are famous for having the largest crystals ever found on Earth; some spodumene crystals in pegmatites have reached lengths of nearly 13 meters.

Field Identification & Locations

Identify in the field by the exceptionally large size of individual mineral grains (quartz, feldspar, and mica) compared to the surrounding rock. Often found in dikes or veins cutting through other rocks.

Identified on: 4/22/2026

Mode: Standard