igneous

Granite

Granite (composed primarily of Quartz, Feldspar, and Mica)

Hardness: 6-7 on Mohs scale; Color: typically mottled grey, white, pink, or black; Luster: vitreous to dull; Crystal structure: phaneritic (coarse-grained); Specific gravity: 2.65 to 2.75.

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

Identified March 29, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: typically mottled grey, white, pink, or black; Luster: vitreous to dull; Crystal structure: phaneritic (coarse-grained); Specific gravity: 2.65 to 2.75.

Formation & geological history

Formed from the slow crystallization of magma below Earth’s surface (intrusive). It is a major component of continental crust and can range from Precambrian to Cenozoic in age.

Uses & applications

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

Geological facts

Mount Rushmore is carved into a granite batholith. Granite is one of the hardest and most durable natural stones, making it the choice for the base of the Statue of Liberty.

Field identification & locations

Identify in the field by its visible, interlocking mineral grains and lack of foliation. Commonly found in mountain ranges and continental shield areas. Look for crystal faces of quartz and feldspar that sparkle in the light.

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