Pegmatite (with smoky quartz and tourmaline/biotite)

Physical Properties

Hardness: 6-7 (Mohs); Color: Mottled gray, smoky brown, and black; Luster: Vitreous to pearly; Crystal structure: Phaneritic (large, visible crystals); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed during the final stages of a magma chamber's crystallization. The high water and mineral content allow crystals to grow exceptionally large over thousands of years.

Uses & Applications

Source of rare earth elements, industrial quartz for electronics, and occasionally used as a decorative building stone or for mineral collecting.

Geological Facts

Pegmatites often contain the largest individual crystals in the world, some reaching several meters in length. They are the primary source for many popular gemstones like aquamarine and tourmaline.

Field Identification & Locations

Identify by the presence of unusually large mineral grains (over 1cm) compared to standard granite. Often found in mountainous regions or shield areas with ancient volcanic history.

Identified on: 4/19/2026

Mode: Standard