igneous

Granite

Granitoid (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8 + SiO2)

Hardness: 6-7 Mohs; Color: Mottled pink, white, gray, and black; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Poor; Specific Gravity: 2.63 to 2.75

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

Identified March 16, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow crystallization of silica-rich magma beneath the Earth's surface (intrusive). They can be found in continental crust dating back billions of years to the Precambrian era.

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 is the most common igneous rock found on Earth's continental surface. The famous peaks of Yosemite National Park (like Half Dome) and Mount Rushmore are made entirely of granite.

Field identification & locations

Identify in the field by the 'salt and pepper' appearance of interlocking crystals of quartz (clear/gray), feldspar (pink/white), and mica (black). Commonly found in mountain ranges or Shield areas. Collectors look for unique inclusions or rare pegmatite formations.

Other igneous specimens

See all

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