Igneous

Granite

Granite (Mainly Quartz SiO2, Feldspar KAlSi3O8, and Mica KAl2(AlSi3O10)(OH)2)

Hardness: 6-7 on Mohs scale; Color: Phaneritic motley of white, gray, and black; Luster: Vitreous to dull; Crystal structure: Coarse-grained granular; Cleavage: None (grains exhibit fracture); Specific Gravity: 2.63 to 2.75

Hardness: 6-7 on Mohs scale
Color: Phaneritic motley of white, gray, and black
Luster: Vitreous to dull

Identified March 16, 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 back to the Precambrian or Paleozoic eras, forming in continental crust above subduction zones.

Uses & applications

Extensively used as a construction material for countertops, floor tiles, paving stone, monuments, and as 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 granite batholith in South Dakota, and the base of the Statue of Liberty is made of granite.

Field identification & locations

Identify in the field by its speckled, 'salt and pepper' appearance and large, visible interlocking crystals of different colors. Commonly found in mountain ranges and glacially drifted areas worldwide.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral