igneous

Granite

Granite (composed primarily of Quartz, Alkali Feldspar, and Plagioclase)

Hardness: 6-7 on Mohs scale; Color: Grayish-white with salt-and-pepper appearance; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: None (fractures); Specific gravity: 2.63 to 2.75

Hardness: 6-7 on Mohs scale
Color: Grayish-white with salt-and-pepper appearance
Luster: Dull to vitreous

Identified February 18, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of magma below Earth's surface (intrusive). Most granites date from the Precambrian to the Cenozoic eras, found in continental crustal plates.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stone, curbing, and monuments. Also used as crushed stone for road base and railroad ballast.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a granite batholith. It is one of the hardest and most durable natural stones available.

Field identification & locations

Identify by its 'salt and pepper' look and visible interlocking crystals. Common in mountain ranges and glacial till. For collectors, look for specimens with large 'phenocrysts' or unique mineral inclusions.

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