igneous

Granite Cobble

Phaneritic Felsic Igneous Rock

Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (mottled grey, white, and black with hints of pink/tan). Luster: Dull (weathered) to vitreous (on fresh breaks). Structure: Coarsely crystalline (phaneritic). Cleavage: None (fractures irregularly). Specific gravity: 2.63 - 2.75.

Hardness: 6-7 on Mohs scale
Luster: Dull (weathered) to vitreous (on fresh breaks)

Identified March 24, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of silica-rich magma deep underground (plutonic formation). This specimen shows rounded edges indicating 'river wear' or glacial transport from its original outcrop. Geological ages for granite can range from the Archean Eon to the Cenozoic Era.

Uses & applications

Used extensively in construction (crushed stone), architecture (countertops, monuments), and as abrasive material. Natural river-rounded granite is often used in landscaping and masonry.

Geological facts

Granite makes up the majority of the Earth's continental crust. Because it forms at great depths, its appearance at the surface is the result of massive tectonic uplift and the erosion of miles of overlying rock.

Field identification & locations

Identify in the field by the 'salt and pepper' look where distinct mineral grains of quartz (clear/grey) and feldspar (white/pink) are visible to the naked eye. This specimen is a common 'river rock' found in glaciated regions or active/ancient riverbeds. Collectors look for unique inclusions or high-contrast coloration.

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mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous