igneous
Pegmatite
Granitic Pegmatite
Hardness: 6-7 (Mohs); Color: white, cream, tan, smoky gray with dark inclusions; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Good in feldspars, none in quartz; Specific gravity: 2.6-2.7
- Hardness
- 6-7 (Mohs)
- Color
- white, cream, tan, smoky gray with dark inclusions
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 (Mohs); Color: white, cream, tan, smoky gray with dark inclusions; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Good in feldspars, none in quartz; 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. Most common in Precambrian and Paleozoic terrains.
Uses & applications
Source of rare earth elements, lithium (spodumene), gemstones like beryl, and industrial minerals like high-purity quartz and feldspar for ceramics and electronics.
Geological facts
Pegmatites are famous for producing the world's largest crystals, sometimes reaching several meters in length. They often contain rare minerals like tourmaline and lepidolite.
Field identification & locations
Identify by the large intergrown crystals of quartz, feldspar, and mica. Look for 'graphic' textures. Found globally in continental shields like the Black Hills (USA) or regions of Brazil.
