igneous
Granite Cobble
Phaneritic Felsic Igneous Rock
Hardness: 6-7 on Mohs scale. Color: Mottled grey, white, and black. Luster: Dull to vitreous. Crystal structure: Phaneritic (visible coarse-grained crystals). Cleavage: Imperfect. Specific Gravity: 2.63 to 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled grey, white, and black
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled grey, white, and black. Luster: Dull to vitreous. Crystal structure: Phaneritic (visible coarse-grained crystals). Cleavage: Imperfect. Specific Gravity: 2.63 to 2.75.
Formation & geological history
Formed from the slow crystallization of magma below Earth's surface. High in silica and alkali metal oxides. This specific specimen shows rounding from water erosion (alluvial or glacial transport).
Uses & applications
Used in construction, aggregate, landscaping, and as a decorative garden stone. Granite is also a major source of dimension stone for countertops and monuments.
Geological facts
Granite makes up a large portion of the continental crust. Because of its hardness, it survives long journeys in rivers, which is why it is often found as smooth cobbles far from its original mountain source.
Field identification & locations
Identify by its 'salt and pepper' appearance and visible interlocking crystals of quartz and feldspar. Found globally in mountainous regions or riverbeds downstream from crystalline basements.
