igneous
Granite Cobble
Phaneritic Felsic Igneous Rock
Hardness: 6-7 on Mohs scale; Color: Mottled pink, gray, and white; Luster: Dull (weathered) to vitreous (on fresh breaks); Crystal Structure: Phaneritic (visible grains of quartz, feldspar, and mica); Specific Gravity: 2.63-2.75
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled pink, gray, and white
- Luster
- Dull (weathered) to vitreous (on fresh breaks)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Mottled pink, gray, and white; Luster: Dull (weathered) to vitreous (on fresh breaks); Crystal Structure: Phaneritic (visible grains of quartz, feldspar, and mica); Specific Gravity: 2.63-2.75
Formation & geological history
Formed from the slow cooling and crystallization of magma deep beneath the Earth's surface (plutonic). This specific specimen has been rounded through fluvial or glacial transport. Age varies by location, often dating from the Precambrian to Cenozoic eras.
Uses & applications
Crushed stone for road base, concrete aggregate, and decorative landscaping. High-quality slabs are used for countertops and monuments.
Geological facts
Granite makes up a large part of the Earth's continental crust. The pink color in this specimen is specifically caused by Potassium Feldspar (orthoclase).
Field identification & locations
Identify by its 'salt and pepper' or mottled appearance and the presence of visible interlocking crystals. Common in riverbeds, glacial till, and mountainous outcrops. It will not react with acid unlike limestone.
