igneous
Pegmatite
Granitic Pegmatite
Hardness: 6-7 Mohs; Color: White, gray, tan, and black; Luster: Vitreous to pearly; Crystal Structure: Very coarse-grained phaneritic; Cleavage: Good in feldspars; Specific Gravity: 2.6-2.7
- Hardness
- 6-7 Mohs
- Color
- White, gray, tan, and black
- Luster
- Vitreous to pearly
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: White, gray, tan, and black; Luster: Vitreous to pearly; Crystal Structure: Very coarse-grained phaneritic; Cleavage: Good in feldspars; Specific Gravity: 2.6-2.7
Formation & geological history
Formed during the final stages of a magma body's crystallization. It originates from water-rich melts that allow for rapid ion migration, resulting in exceptionally large crystals. Found in intrusive igneous environments.
Uses & applications
Source of rare earth elements, industrial minerals like quartz and feldspar, and gemstones such as tourmaline, beryl, and topaz. Used in ceramics and electronics.
Geological facts
Pegmatites are famous for containing the largest crystals ever found on Earth, with some individual crystals reaching over 10 meters in length.
Field identification & locations
Identify by the presence of extremely large, interlocking crystals of quartz, feldspar, and mica. Commonly found in mountains or tectonic shield areas like the Black Hills of South Dakota or Minas Gerais, Brazil.
