igneous

Granite Cobble

Granitoid (typically containing Quartz SiO2, Feldspar KAlSi3O8, and Mica minerals)

Hardness: 6-7 on Mohs scale; Color: Pinkish-tan with visible dark mineral flecks; Luster: Dull (weathered surface); Structure: Phaneritic (coarse-grained) crystalline texture; Cleavage: None (fractures irregularly); Specific Gravity: 2.63 to 2.75.

Hardness: 6-7 on Mohs scale
Color: Pinkish-tan with visible dark mineral flecks
Luster: Dull (weathered surface)

Identified February 19, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow subterranean cooling of silica-rich magma (intrusive igneous). This specific specimen has been rounded by fluvial (river) or glacial transport, a process that can take thousands of years. Its age can range from hundreds of millions to billions of years depending on the source pluton.

Uses & applications

Used widely in construction as crushed stone or aggregate. High-quality samples are used for countertops, curbing, and monuments. Smooth cobbles like this are popular in landscaping and decorative masonry.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Because it is so hard and resistant to erosion, rounded granite cobbles are often found far from their original source, transported by ancient glaciers or floodwaters.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance of interlocking crystals and its extreme hardness (it will scratch glass but not be scratched by a steel blade). Commonly found in riverbeds, glacial moraines, and rocky coastlines.

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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)

mineral

Magnetite

Magnetite (Fe3O4)

mineral