igneous
Granite Cobble
Felsic Intrusive Igneous Rock (Granite)
Hardness: 6-7 on Mohs scale; Color: Mottled white, grey, and black; Luster: Vitreous to dull; Crystal Structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspar, none in quartz; Specific Gravity: 2.65-2.75
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled white, grey, and black
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Mottled white, grey, and black; Luster: Vitreous to dull; Crystal Structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspar, none in quartz; Specific Gravity: 2.65-2.75
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground. This specific specimen shows signs of water-rounding, suggesting it was relocated from its source via a river or glacial process. Ages vary by location, typically ranging from Proterozoic to Cenozoic.
Uses & applications
Used widely in construction as crushed stone, dimension stone for countertops and monuments, and as decorative river rock in landscaping.
Geological facts
Granite makes up a large portion of the Earth's continental crust. The black specks are usually biotite mica or hornblende, while the white/clear parts are quartz and feldspar.
Field identification & locations
Identify by its 'salt and pepper' appearance and visible interlocking crystals. It is found globally in mountainous regions or glacial till. Collectors look for unique mineral inclusions or significant rounding.
