igneous

Granite

Granite (composed primarily of Quartz, Alkali Feldspar, and Plagioclase)

Hardness: 6-7 Mohs; Color: White, gray, or pinkish with black specks; Luster: Vitreous to pearly; Crystal structure: Phaneritic (coarse-grained, visible crystals); Cleavage: Indistinct; Specific Gravity: 2.63 to 2.75

Hardness: 6-7 Mohs
Color: White, gray, or pinkish with black specks
Luster: Vitreous to pearly

Identified April 6, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface (intrusive). It is found in the continental crust and often dates back hundreds of millions to billions of years.

Uses & applications

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

Geological facts

Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in the Black Hills of South Dakota.

Field identification & locations

Identify by its 'salt and pepper' appearance and visible interlocking crystals of quartz and feldspar. Found globally in mountainous regions or areas where ancient crust is exposed.

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