igneous

Granite Cobble

Felsic Intrusive Igneous Rock (composed of Quartz, Alkali Feldspar, and Plagioclase)

Hardness: 6-7 on Mohs scale; Color: Light grey/white peppered with black/dark minerals; Luster: Dull to vitreous; Crystal structure: Phaneritic (visible crystals); Cleavage: None (fractures irregularly); Specific gravity: 2.63 - 2.75

Hardness: 6-7 on Mohs scale
Color: Light grey/white peppered with black/dark minerals
Luster: Dull to vitreous

Identified March 18, 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 (plutonic). This specific specimen shows alluvial rounding, meaning it was transported by water which smoothed its edges over thousands of years.

Uses & applications

Used widely in construction as dimension stone, countertops, and aggregate. Small rounded cobbles like this are common in landscaping and as decorative garden stones.

Geological facts

Granite is the primary rock found in the Earth’s continental crust. Because it is highly resistant to weathering, it often forms the core of many mountain ranges. The pink or white colors come from feldspar, while the clear/glassy parts are quartz.

Field identification & locations

Identify byIts 'salt and pepper' appearance and the presence of visible, interlocking crystals. These are commonly found in riverbeds, glacial tills, or areas with exposed batholiths. It will not be scratched by a steel knife.

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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