igneous
Pegmatite
Igneous Pegmatite (Quartz-Feldspar-Biotite)
Hardness varies by mineral (Quartz is 7, Feldspar is 6 on Mohs scale), color is predominantly pinkish-white with dark accessory minerals, vitreous to pearly luster, coarse-grained crystal structure with exceptionally large crystals, uneven fracture, specific gravity around 2.5 to 2.7.
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Physical properties
Hardness varies by mineral (Quartz is 7, Feldspar is 6 on Mohs scale), color is predominantly pinkish-white with dark accessory minerals, vitreous to pearly luster, coarse-grained crystal structure with exceptionally large crystals, uneven fracture, specific gravity around 2.5 to 2.7.
Formation & geological history
Formed from cooling magma deep within the Earth's crust during the final stages of crystallization, heavily enriched in water and incompatible elements, allowing very large crystals to grow.
Uses & applications
Source of rare earth elements, gemstone mining (tourmaline, beryl, topaz), and industrial minerals like high-purity quartz and feldspar for ceramics.
Geological facts
Pegmatites can host some of the largest individual crystals ever found on Earth, sometimes measuring several meters in length.
Field identification & locations
Easily identified in the field by its extremely coarse grain size (phaneritic) compared to surrounding standard intrusive rocks like granite, often found in ancient cratons and mountain-building belts.
