igneous

Granite Cobble

Granite (Phaneritic Quartz-Feldspar Felsic Rock)

Hardness: 6-7 on Mohs scale; Color: Pinkish-tan with gray and black specks; Luster: Dull (weathered) to vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: None (grains exhibit fracture); Specific gravity: 2.63 to 2.75

Hardness: 6-7 on Mohs scale
Color: Pinkish-tan with gray and black specks
Luster: Dull (weathered) to vitreous

Identified March 19, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of silica-rich magma beneath the Earth's surface. High levels of intrusive pressure allow for large mineral crystals. Geological age varies significantly but granite is common in Precambrian to Mesozoic crustal formations. This specific specimen has been further shaped by fluvial or glacial erosion into a smooth cobble.

Uses & applications

Used widely in construction (crushed stone), architecture (countertops, monuments), and dimension stone. Water-worn cobbles like this are often used in landscaping and xeriscaping.

Geological facts

Granite is the primary rock of the Earth's continental crust. Its pink color usually comes from orthoclase feldspar, while the clear/gray glassy parts are quartz and black specks are biotite or hornblende. It is exceptionally resistant to weathering compared to many other rocks.

Field identification & locations

Identify in the field by looking for a 'salt and pepper' appearance with visible crystals (pink, white, and black). Common in riverbeds, glacial tills, and mountain ranges. For collectors, look for unique mineral inclusions or vein patterns.

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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

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Magnetite

Magnetite (Fe3O4)

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