igneous

Granite

Plutonic Igneous Rock (composed of Quartz, Feldspar, and Mica)

Hardness: 6-7 on Mohs scale. Color: Mottled buff, pink, white, and gray with dark specks. Luster: Vitreous to dull. Structure: Phaneritic (coarse-grained) crystalline. Cleavage: Indistinct in bulk, but feldspar grains show two planes at 90 degrees.

Hardness: 6-7 on Mohs scale
Color: Mottled buff, pink, white, and gray with dark specks
Luster: Vitreous to dull

Identified March 31, 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 from Archean to Cenozoic depending on the specific batholith; common in continental crust platforms.

Uses & applications

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

Geological facts

Granite makes up the majority of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in South Dakota. Because it contains trace amounts of uranium, some granite can emit small amounts of radon gas.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals of quartz (translucent) and feldspar (opaque/pink/white). Common in mountainous regions and shield areas. It is very resistant to weathering.

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