igneous

Granite

Phaneritic Intrusive Igneous Rock (primarily Quartz, Feldspar, and Mica)

Hardness: 6-7 Mohs; Color: Pink, white, and black mottled patterns; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained coarse crystals); Cleavage: Dependent on internal minerals (Feldspar has two directions, Mica has one); Specific Gravity: 2.63 to 2.75

Hardness: 6-7 Mohs
Color: Pink, white, and black mottled patterns
Luster: Vitreous to dull

Identified March 20, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep beneath the Earth's surface (plutonic). Because it cools slowly, large individual mineral crystals grow. It is found in continental crust and dates back billion of years (Precambrian) to more recent tectonic events.

Uses & applications

Extensively used in construction for countertops, floor tiles, and paving stones. Also used in monuments, curbing, and as crushed stone for road base. Higher quality specimens are polished for interior design.

Geological facts

Granite makes up the majority of the Earth's continental crust. Mount Rushmore is carved into a granite batholith. It is one of the hardest and most durable common stones, resistant to weathering and acid.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals. Look for the distinctive pink/orange of Orthoclase Feldspar, translucent grey of Quartz, and black flakes of Biotite or Hornblende. Common in mountain ranges and glacial deposits.

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

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral