igneous
Granite Pebble (Salt and Pepper Granite)
Felsic Intrusive Igneous Rock (Granite)
Hardness: 6-7 on Mohs scale. Color: Mottled white and tan with dark brown/black spots (salt and pepper appearance). Luster: Dull (weathered) to vitreous (on fresh breaks). Crystal structure: Phaneritic (visible interlocking crystals of quartz, feldspar, and biotite). Cleavage: None (fractures irregularly).…
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull (weathered) to vitreous (on fresh breaks)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled white and tan with dark brown/black spots (salt and pepper appearance). Luster: Dull (weathered) to vitreous (on fresh breaks). Crystal structure: Phaneritic (visible interlocking crystals of quartz, feldspar, and biotite). Cleavage: None (fractures irregularly). Specific gravity: 2.63 to 2.75.
Formation & geological history
Formed through the slow cooling and crystallization of silica-rich magma deep beneath the Earth's crust (plutonic formation). This specific specimen has been rounded by mechanical weathering, likely in a river or coastal environment. Geological age can range from billions of years (Precambrian) to as recent as the Cenozoic depending on the source batholith.
Uses & applications
Used extensively in construction (aggregate, dimension stone), kitchen countertops, and monuments because of its durability. In this pebble form, it is commonly used for landscaping, decorative garden paths, or as aquarium gravel.
Geological facts
Granite makes up the majority of the Earth's continental crust. Unlike oceanic crust (basalt), granite is less dense, allowing continents to 'float' higher on the mantle. The dark spots in this 'salt and pepper' variety are typically mica or amphibole minerals.
Field identification & locations
Identify in the field by its speckled appearance of light and dark minerals and its high hardness (it will easily scratch glass). It is found globally across all continental landmasses, particularly in mountainous regions and glacial deposits. For collectors, look for high-contrast grain patterns or large mineral inclusions.
