igneous
Granitic Pegmatite
Phaneritic Granite with Potassium Feldspar (KAlSi3O8), Quartz (SiO2), and Plagioclase
Hardness: 6-7 (Mohs scale); Color: Mottled pink, grey, and white; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Two directions at 90 degrees in feldspar; Specific gravity: 2.6-2.7.
- Hardness
- 6-7 (Mohs scale)
- Color
- Mottled pink, grey, and white
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Mottled pink, grey, and white; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Two directions at 90 degrees in feldspar; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the slow cooling and crystallization of magma deep beneath the Earth's surface during the final stages of a magma chamber's crystallization. Commonly associated with tectonic plate boundaries or ancient continental shields.
Uses & applications
Used primarily in construction as crushed stone for road base or architectural building stone. High-quality pieces are used for countertops or as sources for industrial crystals (quartz/feldspar).
Geological facts
Pegmatites are famous for containing exceptionally large crystals, sometimes reaching several meters in length, due to the high water content in the magma lowering viscosity during formation.
Field identification & locations
Identify in the field by its very large (over 1cm) interlocking crystals and distinct pink color from orthoclase feldspar. Common in mountainous regions like the Appalachians, Rockies, or Canadian Shield. Collectors look for accessory minerals like tourmaline or beryl.
