igneous

Granite

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

Hardness: 6-7 on Mohs scale; Color: typically mottled grey, white, pink, or tan with black specks; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic texture; Cleavage: None (it fractures); Specific gravity: 2.63 - 2.75.

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

Identified March 25, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of silica-rich magma deep underground (plutonic). It can form during any geological era but is a primary component of continental crust. It takes millions of years to cool, allowing for visible crystals.

Uses & applications

Extensively used as dimension stone in construction for countertops, floor tiles, and monuments. Also used in crushed form for road base and railroad ballast. Highly valued as a durable decorative stone.

Geological facts

Granite makes up a large part of the Earth's continental crust. Mount Rushmore is carved into a granite batholith. It is one of the hardest and most durable natural stones, which is why it has been used in architecture since Ancient Egypt.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and large, interlocked visible crystals. It is found in mountain ranges and Shields (like the Canadian Shield). Look for lack of layering and a very hard surface that cannot be scratched by a steel knife.

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