igneous

Granite

Granite (compositionally of Quartz, Alkali Feldspar, and Plagioclase)

Hardness: 6-7 on Mohs scale; Color: typically white, gray, or pink with dark specks; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Indistinct; Specific gravity: 2.63 to 2.75

Hardness: 6-7 on Mohs scale
Color: typically white, gray, or pink with dark specks
Luster: Vitreous to dull

Identified May 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface (intrusive). It is predominantly of Phanerozoic age but can be found in ancient cratons over 3 billion years old.

Uses & applications

Widely used in construction, countertops, flooring, monuments, and as crushed stone for road base.

Geological facts

Granite makes up a large portion of the Earth's continental crust. It is extremely durable and iconic for being the rock used in Mount Rushmore.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals. Common in mountain ranges and continental shield areas. Look for visible flakes of mica and glassy quartz.

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