igneous

Granite Cobble

Felsic Intrusive Igneous Rock (Granite)

Hardness: 6-7 on Mohs scale; Color: Mottled white, grey, and black; Luster: Vitreous to dull; Crystal Structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspar, none in quartz; Specific Gravity: 2.65-2.75

Hardness: 6-7 on Mohs scale
Color: Mottled white, grey, and black
Luster: Vitreous to dull

Identified March 27, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep underground. This specific specimen shows signs of water-rounding, suggesting it was relocated from its source via a river or glacial process. Ages vary by location, typically ranging from Proterozoic to Cenozoic.

Uses & applications

Used widely in construction as crushed stone, dimension stone for countertops and monuments, and as decorative river rock in landscaping.

Geological facts

Granite makes up a large portion of the Earth's continental crust. The black specks are usually biotite mica or hornblende, while the white/clear parts are quartz and feldspar.

Field identification & locations

Identify by its 'salt and pepper' appearance and visible interlocking crystals. It is found globally in mountainous regions or glacial till. Collectors look for unique mineral inclusions or significant rounding.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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