igneous
Granitic Pegmatite
Pegmatite
Hardness: 6-7 (Mohs scale); Color: Pink/flesh (Potassium Feldspar), white/gray (Quartz), and silver/green (Mica); Luster: Vitreous to pearly; Crystal structure: Very large, interlocking crystals (phaneritic); Cleavage: Perfect in feldspar and mica, none in quartz.
- Hardness
- 6-7 (Mohs scale)
- Luster
- Vitreous to pearly
Identified More igneous →
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Pink/flesh (Potassium Feldspar), white/gray (Quartz), and silver/green (Mica); Luster: Vitreous to pearly; Crystal structure: Very large, interlocking crystals (phaneritic); Cleavage: Perfect in feldspar and mica, none in quartz.
Formation & geological history
Formed during the final stages of a magma's crystallization. Highly fluid, water-rich melts allow ions to move quickly and form exceptionally large crystals. Typically found in batholiths or as dikes and sills.
Uses & applications
Primary source of industrial minerals (feldspar, quartz, mica) and rare elements (lithium, tantalum). Used as decorative dimension stone and for gemstone extraction.
Geological facts
Pegmatites are famous for producing the world's largest crystals, sometimes reaching several meters in length. Many of the Earth's finest gemstones, such as tourmaline, beryl, and topaz, are found exclusively in pegmatite pockets.
Field identification & locations
Identify in the field by the exceptionally large grain size compared to surrounding rock. Look for interlocking pink feldspar and glassy quartz. Found in mountainous regions with exposed continental crust like the Black Hills of South Dakota or the Appalachian Mountains.
