igneous
Biotite Granite
Phaneritic Felsic Igneous Rock
Hardness: 6-7 (Mohs); Color: Salt and pepper (white, gray, black, brown); Luster: Vitreous to pearly; Crystal structure: Phaneritic (medium to coarse grained); Specific Gravity: 2.6-2.7
- Hardness
- 6-7 (Mohs)
- Color
- Salt and pepper (white, gray, black, brown)
- Luster
- Vitreous to pearly
Identified More igneous →
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Physical properties
Hardness: 6-7 (Mohs); Color: Salt and pepper (white, gray, black, brown); Luster: Vitreous to pearly; Crystal structure: Phaneritic (medium to coarse grained); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the slow cooling and crystallization of magma deep beneath the Earth's surface (plutonic). Found in continental crust throughout geological history from Archean to Cenozoic.
Uses & applications
Used widely in construction as dimension stone, countertops, floor tiles, and as crushed stone for road aggregate.
Geological facts
Granite makes up the majority of the Earth's continental crust. The dark flakes seen here are Biotite mica, which gives the rock its speckled appearance.
Field identification & locations
Identify in the field by its interlocking crystalline texture and lack of foliation. Common in mountain ranges and eroded crystalline shields. Look for the 'sparkle' of mica flakes among quartz and feldspar.
