igneous
Granitic Pegmatite
Coarse-grained Granite (KAlSi3O8 + SiO2)
Hardness: 6-7 (Mohs scale); Color: Pink/Salmon (Potassium Feldspar) and Grayish-White (Quartz); Luster: Vitreous to pearly; Structure: Phaneritic/Pegmatitic (exceptionally large crystals); Cleavage: Perfect in two directions for feldspar, none for quartz.
- Hardness
- 6-7 (Mohs scale)
- Color
- Pink/Salmon (Potassium Feldspar) and Grayish-White (Quartz)
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Pink/Salmon (Potassium Feldspar) and Grayish-White (Quartz); Luster: Vitreous to pearly; Structure: Phaneritic/Pegmatitic (exceptionally large crystals); Cleavage: Perfect in two directions for feldspar, none for quartz.
Formation & geological history
Formed during the final stages of a magma's crystallization, where high water content allows large crystals to grow rapidly. Typically found in batholiths or as dikes/veins within older rock layers, dating from various geological eras depending on location.
Uses & applications
Used as a source of industrial minerals (feldspar and quartz), crushed stone for construction, and sometimes mined for rare earth elements or gemstones. High-quality pieces are used in architectural stone (granite countertops).
Geological facts
Pegmatites are famous for growing the largest crystals on Earth, sometimes reaching over 30 feet in length. The pink color is specifically due to Potassium Feldspar (Orthoclase), while the translucent gray parts are Milky Quartz.
Field identification & locations
Identify in the field by the distinct interlocking of very large pink and white crystals. It is commonly found in mountainous regions or shield areas like the Rockies, Appalachians, or Scandinavian Shield. Use a scratch test; it will easily scratch glass.
