igneous
Pegmatite
Granitic Pegmatite
Hardness (Mohs scale): 6-7; Color: Pinkish-brown (feldspar), grey/clear (quartz), black (accessory minerals); Luster: Vitreous to pearly; Crystal structure: Very coarse-grained (phaneritic); Cleavage: Good in feldspar grains; Specific gravity: 2.6-2.7
- Luster
- Vitreous to pearly
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Physical properties
Hardness (Mohs scale): 6-7; Color: Pinkish-brown (feldspar), grey/clear (quartz), black (accessory minerals); Luster: Vitreous to pearly; Crystal structure: Very coarse-grained (phaneritic); Cleavage: Good in feldspar grains; Specific gravity: 2.6-2.7
Formation & geological history
Formed during the final stages of a magma's crystallization, usually in hydrothermal or intrusive environments where high water content allows for the growth of exceptionally large crystals. Most common in Precambrian or Paleozoic shields.
Uses & applications
Source of rare earth elements, industrial minerals like quartz and feldspar, and gemstones such as tourmaline, beryl, and spodumene.
Geological facts
Pegmatites are famous for holding the world's largest crystals; some spodumene and beryl crystals in pegmatites have been recorded at over 10 meters long.
Field identification & locations
Identify in the field by searching for exceptionally large, interlocking crystals of quartz and feldspar within granitic terrain. They often form dikes or veins cutting through smaller-grained igneous rocks.
