igneous

Granite Cobble

Phaneritic Felsic Igneous Rock (Granite)

Hardness: 6-7 on Mohs scale; Color: salt-and-pepper appearance with grey, white, and black grains; Luster: dull on weathered surface, vitreous when broken; Crystal Structure: phaneritic (visible interlocking crystals); Cleavage: none (fractures irregularly).

Hardness: 6-7 on Mohs scale
Luster: dull on weathered surface, vitreous when broken

Identified March 26, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep within the Earth's crust. This specimen has been rounded into a cobble shape by mechanical weathering in high-energy environments like rivers or coastal beaches over thousands of years.

Uses & applications

In this rounded form, it is used for landscaping, decorative stone mulch, and water features. In raw blocks, granite is the primary material for countertops, monuments, and heavy construction.

Geological facts

Granite makes up the majority of the Earth's continental crust. Because it is resistant to acid rain and very durable, it has been used since ancient Egypt for monumental architecture, including parts of the Great Pyramid of Giza.

Field identification & locations

Identify by its 'salt and pepper' crystalline texture; unlike sedimentary rocks, it won't show layers. Common in glaciated regions or riverbeds downstream from mountain ranges. Collectors look for unique inclusions or high pink orthoclase content.

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

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Magnetite

Magnetite (Fe3O4)

mineral