igneous
Granite
Granite (Felsic Plutonic Rock)
Hardness: 6-7 on Mohs scale. Color: can range from white/gray to pink/tan with black specks. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained visible crystals). Cleavage: Varies by mineral constituent (feldspar has 2 planes, quartz has none). Specific Gravity: 2.63 - 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- can range from white/gray to pink/tan with black specks
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale. Color: can range from white/gray to pink/tan with black specks. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained visible crystals). Cleavage: Varies by mineral constituent (feldspar has 2 planes, quartz has none). Specific Gravity: 2.63 - 2.75.
Formation & geological history
Formed through the slow crystallization of magma below the Earth's surface (intrusive). Most granites date from the Precambrian to Cenozoic eras, typically found in continental crust and mountain ranges.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments. Also used as crushed stone for road base and railroad ballast.
Geological facts
Granite is the most common igneous rock found on the Earth's surface. Mount Rushmore is carved into a granite batholith, and it is a primary component of the continental crust.
Field identification & locations
Identify by its interlocking 'salt and pepper' appearance of quartz (clear/gray), feldspar (white/pink), and mica (black/shiny). Found in terminal moraines, mountain cores, and outcrops. Collectors look for unique large-crystal varieties (pegmatites).
