igneous

Granite Cobble

Granite

Hardness: 6-7 on Mohs scale. Color: Mottled pink, grey, and black. Luster: Dull to vitreous. Structure: Phaneritic (medium-grained crystalline). Composition: Quartz, alkali feldspar, and plagioclase.

Hardness: 6-7 on Mohs scale
Color: Mottled pink, grey, and black
Luster: Dull to vitreous

Identified May 27, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale. Color: Mottled pink, grey, and black. Luster: Dull to vitreous. Structure: Phaneritic (medium-grained crystalline). Composition: Quartz, alkali feldspar, and plagioclase.

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface (intrusive). This specific specimen has been rounded into a 'cobble' or 'river rock' shape by water erosion or glacial transport over thousands of years.

Uses & applications

Used in construction, aggregate, landscaping, and as a decorative stone. High-quality slabs are used for countertops.

Geological facts

Granite makes up much of the Earth's continental crust. It is one of the hardest and most durable common rocks, which is why it is used for monuments.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals. Common in mountain ranges and riverbeds. This rounded shape indicates it has traveled far from its source.

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Fluorapatite (Ca5(PO4)3F)

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