igneous
Granite Pegmatite
Pegmatite (Fulgite / Felsic Intrusive Rock)
Hardness of 6-7 on Mohs scale due to quartz and feldspar content; color ranges from off-white and pinkish to tan with dark mineral inclusions; vitreous to pearly luster; coarse-grained crystal structure with interlocking crystals; specific gravity around 2.5-2.7.
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Physical properties
Hardness of 6-7 on Mohs scale due to quartz and feldspar content; color ranges from off-white and pinkish to tan with dark mineral inclusions; vitreous to pearly luster; coarse-grained crystal structure with interlocking crystals; specific gravity around 2.5-2.7.
Formation & geological history
Formed from the cooling of silica-rich magma deep within the Earth's crust, often associated with the final stages of magma crystallization where water and other volatiles allow very large crystals to grow.
Uses & applications
Used as a source for rare minerals, gemstone mining (such as tourmaline, beryl, and topaz), and occasionally crushed for aggregate stone.
Geological facts
Pegmatites are famous for containing some of the largest individual crystals ever found on Earth, sometimes measuring many meters in length.
Field identification & locations
Easily identified in the field by its extremely coarse-grained texture (phaneritic) where individual mineral crystals like quartz and feldspar are exceptionally large and visible to the naked eye.
