igneous
Pegmatite
Granitic Pegmatite
Hardness: 6.0-7.0 (average); Color: Mixed white, gray, beige, with black inclusions; Luster: Vitreous to pearly (mica); Crystal structure: Phaneritic (very large crystals); Cleavage: Perfect in mica flakes, poor in quartz.
- Hardness
- 6
- Color
- Mixed white, gray, beige, with black inclusions
- Luster
- Vitreous to pearly (mica)
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Physical properties
Hardness: 6.0-7.0 (average); Color: Mixed white, gray, beige, with black inclusions; Luster: Vitreous to pearly (mica); Crystal structure: Phaneritic (very large crystals); Cleavage: Perfect in mica flakes, poor in quartz.
Formation & geological history
Formed during the final stages of a magma's crystallization. Highly fluid, water-rich melt allows crystals to grow to exceptional sizes, often in dikes or veins. Usually Precambrian to Cenozoic in age.
Uses & applications
Source of rare earth elements, lithium, gemstones (beryl, tourmaline), and industrial minerals like mica and feldspar. Used in high-end construction and electronics.
Geological facts
Pegmatites contains the largest crystals ever found on Earth, some reaching several meters in length. They are essentially 'giant-grained' granites.
Field identification & locations
Look for exceptionally large mineral grains (over 1cm) compared to surrounding rock. Commonly found in batholith margins. Identification relies on the presence of large plates of mica and blocky feldspar.
