Igneous
Granitic Pegmatite
Granite Pegmatite (typically containing Quartz SiO2, Feldspar KAlSi3O8, and Muscovite)
Hardness (Mohs): 6-7; Color: Mottled white, tan, and brown/grey; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Perfect in mica/feldspar components; Specific gravity: 2.6-2.7
- Color
- Mottled white, tan, and brown/grey
- Luster
- Vitreous to pearly
Identified More igneous →
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Physical properties
Hardness (Mohs): 6-7; Color: Mottled white, tan, and brown/grey; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Perfect in mica/feldspar components; Specific gravity: 2.6-2.7
Formation & geological history
Formed during the final stages of a magma's crystallization, usually in intrusive igneous environments. Water-rich fluids allow for the growth of very large crystals. These can date from the Archean to the Cenozoic era.
Uses & applications
Used as a source of rare earth elements, industrial minerals like mica and feldspar, and occasionally as structural stone or high-end countertops if found in large slabs.
Geological facts
Pegmatites are famous for containing the world's largest individual crystals, sometimes measuring several meters in length. They are the primary source of many gemstones like tourmaline, beryl, and topaz.
Field identification & locations
Identify by the exceptionally large crystal size relative to surrounding rocks (usually >1cm). Found in tectonic belts and near large granitic batholiths. Collectors look for 'vugs' or pockets containing well-formed crystals.
