igneous

Granite

Phaneritic plutonic rock (dominated by SiO2, Al2O3, K2O, Na2O)

Hardness: 6-7 on Mohs scale; Color: typically mottled pink, white, gray, and black; Luster: vitreous to dull; Crystal structure: phaneritic (coarsegrained) with visible crystals of quartz, feldspar, and mica; Specific gravity: 2.63 to 2.75.

Hardness: 6-7 on Mohs scale
Color: typically mottled pink, white, gray, and black
Luster: vitreous to dull

Identified March 20, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of silica-rich magma beneath the Earth's surface. Most granite dates back to the Precambrian or Paleozoic eras, forming at depths of several kilometers under high pressure and temperature.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, and monuments. Also used as crushed stone (aggregate) for road base and concrete.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in the Black Hills of South Dakota. It is one of the hardest and most durable natural stones used by humans.

Field identification & locations

Identify by its 'salt and pepper' appearance and large, interlocking visible crystals. Look for translucent quartz grains and blocky, opaque feldspar. Found globally in continental mountain ranges and shield areas like the Canadian Shield or the Appalachians.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

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

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral