igneous

Granite

Phaneritic Felsic Igneous Rock (primarily SiO2, Al2O3, K2O, Na2O)

Hardness: 6 to 7 on the Mohs scale
Luster: Vitreous to pearly

Identified March 23, 2026More igneous →

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Physical properties

Hardness: 6 to 7 on the Mohs scale. Color: Salt-and-pepper appearance with shades of white, pink, and grey. Luster: Vitreous to pearly. Crystal structure: Phaneritic (coarse-grained) with interlocking crystals of quartz, feldspar, and mica. Cleavage: Indistinct in the mass, but feldspar components show two directions at 90 degrees. Specific gravity: 2.63 to 2.75.

Formation & geological history

Formed through the slow crystallization of magma below the Earth's surface (intrusive). Geological ages vary widely from the Archean Eon to the Cenozoic. It is commonly found in the continental crust within batholiths and mountain ranges.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, and masonry. It is also used in monument carving, curling stones, and as a popular landscaping material.

Geological facts

Granite makes up the majority of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in the Black Hills of South Dakota. Historically, it was used by Ancient Egyptians to build the internal chambers of the Great Pyramid of Giza.

Field identification & locations

Identify in the field by its speckled, interlocking crystal texture where individual minerals (clear quartz, white/pink feldspar, black biotite) are visible to the naked eye. It is found in tectonic regions and ancient shield areas like the Canadian Shield or the Appalachians.

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