igneous
Granite (Granitic Pegmatite/Porphyry)
Felsic intrusive igneous rock (Quartz, Feldspar, Mica composition)
Hardness: 6-7 Mohs; Color: Tan, white, grey, and black speckles; Luster: Vitreous to pearly; Crystal structure: Phaneritic (large visible crystals), primarily hexagonal quartz and monoclinic/triclinic feldspars; Specific gravity: 2.63 to 2.75.
- Hardness
- 6-7 Mohs
- Color
- Tan, white, grey, and black speckles
- Luster
- Vitreous to pearly
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Tan, white, grey, and black speckles; Luster: Vitreous to pearly; Crystal structure: Phaneritic (large visible crystals), primarily hexagonal quartz and monoclinic/triclinic feldspars; Specific gravity: 2.63 to 2.75.
Formation & geological history
Formed through the slow crystallization of magma below Earth's surface. This specimen shows a porphyritic or pegmatitic texture, indicating a multi-stage cooling process where some crystals grew larger than the surrounding matrix.
Uses & applications
Construction (countertops, flooring), monuments, curbing, and crushed stone for road aggregate. Highly valued for durability and resistance to abrasion.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Over long periods of time, the radioactive decay of uranium in granite can lead to the accumulation of radon gas in buildings built over granitic bedrock.
Field identification & locations
Identify in the field by the 'salt and pepper' appearance and hardness (it will scratch glass). It is commonly found in the cores of mountain ranges and stable continental shields (cratons). Check for interlocking crystalline textures rather than layers.
