igneous
Pegmatite (Granitic Pegmatite with Quartz, Feldspar, and Mica)
Granitic Pegmatite
Coarse-grained intrusive igneous rock. Hardness: ~6-7 on Mohs scale (quartz and feldspar dominated). Color: Off-white, pale pink, tan, with silvery shiny mica flakes. Luster: Vitreous to pearly on mica cleavage faces. Structure: Very large intergrown crystals.…
- Hardness
- ~6-7 on Mohs scale (quartz and feldspar dominated)
- Color
- Off-white, pale pink, tan, with silvery shiny mica flakes
- Luster
- Vitreous to pearly on mica cleavage faces
Identified More igneous →
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Physical properties
Coarse-grained intrusive igneous rock. Hardness: ~6-7 on Mohs scale (quartz and feldspar dominated). Color: Off-white, pale pink, tan, with silvery shiny mica flakes. Luster: Vitreous to pearly on mica cleavage faces. Structure: Very large intergrown crystals. Cleavage: Perfect 1-direction cleavage visible in mica books.
Formation & geological history
Formed during the final stages of a magma body's crystallization, where water-rich residual fluids allow large crystals to grow rapidly. Commonly associated with continental crust and mountain-building zones.
Uses & applications
Major source of industrial minerals including sheet mica, potassium feldspar, and quartz. Also harvested for rare elements like lithium, beryllium, and tantalum, as well as mineral specimen collecting.
Geological facts
Pegmatites contain the largest known crystals on Earth, sometimes reaching over 30 feet in length! They often host rare gem minerals like beryl (emerald, aquamarine), tourmaline, and topaz.
Field identification & locations
Identified by extraordinarily large crystal sizes compared to standard granite, featuring distinct reflective metallic-looking mica flakes and milky/translucent quartz patches. Commonly found in pegmatite dikes within granitic terrains.
