igneous
Pegmatite
Igneous Pegmatite
Hardness: 6-7 on Mohs scale (due to dominant quartz and feldspar content); Color: White, pinkish, or off-white with contrasting darker mineral inclusions; Luster: Vitreous to pearly; Crystal structure: Extremely coarse-grained with interlocking crystals; Cleavage: Good in feldspars, none in quartz;…
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 on Mohs scale (due to dominant quartz and feldspar content); Color: White, pinkish, or off-white with contrasting darker mineral inclusions; Luster: Vitreous to pearly; Crystal structure: Extremely coarse-grained with interlocking crystals; Cleavage: Good in feldspars, none in quartz; Specific gravity: 2.5 - 2.8
Formation & geological history
Formed from the cooling of the final, water-rich phases of a magma chamber, allowing very large crystals to grow rapidly in subterranean pockets. Geological age varies widely depending on the host orogenic belt.
Uses & applications
Source of rare earth elements, lithium minerals, industrial feldspar and quartz, and occasionally gem-quality crystals such as tourmaline, beryl, and topaz.
Geological facts
Pegmatites are famous for containing some of the largest individual crystals ever found on Earth, sometimes measuring many meters in length.
Field identification & locations
Easily identified in the field by its exceptionally coarse-grained texture (interlocking crystals usually larger than 2.5 cm) composed predominantly of quartz, feldspar, and mica. Commonly found intruding into larger plutonic bodies or surrounding metamorphic rocks.
