igneous

Granite

Phaneritic plutonic igneous rock (SiO2 range 65-75%)

Hardness: 6-7 Mohs; Color: Gray, pinkish-tan, and white with dark flecks; Luster: Dull (weathered) to vitreous (crystals); Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.63 to 2.75

Hardness: 6-7 Mohs
Color: Gray, pinkish-tan, and white with dark flecks
Luster: Dull (weathered) to vitreous (crystals)

Identified May 31, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep underground (plutonic). This sample appears to be a water-worn river cobble or glacial erratic, likely dating from the Precambrian to Cenozoic depending on location.

Uses & applications

Used extensively in construction (aggregate), architectural facades, countertops, and paving. Highly valued for durability and resistance to weathering.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in South Dakota.

Field identification & locations

Identify by its interlocking salt-and-pepper appearance and visible individual crystals of quartz, feldspar, and mica. Commonly found in mountainous regions or as rounded stones in stream beds.

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Granite

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Granite

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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Dalmatian Jasper

Aplite with Arfvedsonite inclusions

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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)

mineral