igneous

Granite

Phaneritic Felsic Igneous Rock (composed primarily of Quartz, Feldspar, and Mica)

Hardness: 6-7 (Mohs scale); Color: Salt and pepper/speckled grey, white, and black; Luster: Vitreous to dull; Crystal structure: Phaneritic (visible crystals); Specific gravity: 2.63 - 2.75

Hardness: 6-7 (Mohs scale)
Color: Salt and pepper/speckled grey, white, and black
Luster: Vitreous to dull

Identified April 2, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs scale); Color: Salt and pepper/speckled grey, white, and black; Luster: Vitreous to dull; Crystal structure: Phaneritic (visible crystals); Specific gravity: 2.63 - 2.75

Formation & geological history

Formed through the slow crystallization of magma below the Earth's surface in continental crust plumes. These intrusive rocks can be hundreds of millions of years old and are exposed after long periods of erosion.

Uses & applications

Commonly used in construction for countertops, floor tiles, paving stones, and memorial monuments due to its durability and resistance to weathering.

Geological facts

Granite makes up much 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 in the field by its interlocking visible grains of glassy quartz, opaque white/pink feldspar, and black mica flakes. It is very hard and will scratch glass easily.

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