igneous

Granite

Phaneritic Igneous Rock (composed primarily of Quartz SiO2, Alkali Feldspar, and Plagioclase)

Hardness: 6-7 on Mohs scale. Color: Mottled pink, white, gray, and black. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarsegrained). Cleavage: None (though individual feldspar grains exhibit cleavage). Specific gravity: 2.63 to 2.75.

Hardness: 6-7 on Mohs scale
Color: Mottled pink, white, gray, and black
Luster: Vitreous to dull

Identified March 21, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface (intrusive). Geological age varies globally from billions of years (Archean) to more recent eras, typically forming in continental crust above subduction zones.

Uses & applications

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

Geological facts

Granite makes up much of the Earth's continental crust. Famous landmarks like Mount Rushmore and Yosemite's El Capitan are composed of granite. It is one of the hardest and most durable natural stones used by humans.

Field identification & locations

Identify by its 'salt and pepper' look and visible interlocking crystals. Look for translucent quartz, opaque white/pink feldspar, and dark biotite or hornblende. Commonly found in mountain ranges and Shields (like the Canadian Shield).

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