igneous
Granite Pegmatite
Granitic Pegmatite (composition: SiO2 with KAlSi3O8)
Hardness: 6-7 Mohs; Color: Pink, white, and translucent grey; Luster: Vitreous to pearly; Crystal structure: Very large, interlocking crystals of quartz and feldspar; Cleavage: Good in feldspar grains, none in quartz; Specific gravity: 2.6-2.7
- Hardness
- 6-7 Mohs
- Color
- Pink, white, and translucent grey
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 Mohs; Color: Pink, white, and translucent grey; Luster: Vitreous to pearly; Crystal structure: Very large, interlocking crystals of quartz and feldspar; Cleavage: Good in feldspar grains, none in quartz; Specific gravity: 2.6-2.7
Formation & geological history
Formed during the final stages of a magma chamber's crystallization where high water content allows for the growth of exceptionally large crystals. These are typically found in batholiths and dikes and can range from Proterozoic to Cenozoic in age.
Uses & applications
Used as an industrial source of rare elements (lithium, tantalum), high-purity quartz for electronics, potash feldspar for ceramics, and as decorative dimension stone.
Geological facts
Pegmatites are famous for containing the world's largest crystals, sometimes reaching several meters in length. They are the primary source of many gemstones like beryl (emerald/aquamarine) and tourmaline.
Field identification & locations
Identify by exceptionally large crystal size (over 1 cm) and mineralogy (quartz and pink orthoclase). Look for them in vein-like structures or 'dikes' cutting through larger granite bodies.
