igneous
Pegmatite (Granitic)
Granite Pegmatite
Hardness: 6-7 (Mohs); Color: Off-white, tan, and black; Luster: Vitreous to pearly; Crystal Structure: Phaneritic/Very coarse-grained; Cleavage: Varies by mineral (perfect on mica planes); Specific Gravity: 2.6-2.7
- Hardness
- 6-7 (Mohs)
- Color
- Off-white, tan, and black
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 (Mohs); Color: Off-white, tan, and black; Luster: Vitreous to pearly; Crystal Structure: Phaneritic/Very coarse-grained; Cleavage: Varies by mineral (perfect on mica planes); Specific Gravity: 2.6-2.7
Formation & geological history
Formed during the final stages of a magma chamber's crystallization when high water content allows for the growth of exceptionally large crystals. Typically found in plutonic environments often associated with batholiths.
Uses & applications
Source of rare earth elements, industrial minerals like feldspar and mica, and occasional gemstones like tourmaline, beryl, or garnet.
Geological facts
Pegmatites are famous for containing the largest individual crystals ever found on Earth, reaching lengths of over 10 meters in some rare cases.
Field identification & locations
Identify by the extremely large crystal size (usually >1cm) compared to standard granite. Look for clear quartz grains, white/pink feldspar, and dark biotite or tourmaline laths. Widely found in mountain ranges and ancient shields.
