igneous

Granite

Intrusive Igneous Rock (composed primarily of Quartz: SiO2, Feldspar: KAlSi3O8, and Mica: KAl2(AlSi3O10)(OH)2)

Hardness: 6-7 on Mohs scale; Color: Phaneritic (visible grains) pattern with white, grey, pink, and black; Luster: Vitreous to dull; Structure: Granular/crystalline; Cleavage: None (bulk rock), Feldspars show cleavage; Gravity: 2.63 - 2.75

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

Identified March 30, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface. It is an intrusive rock found in continental crust across all geological ages, especially in Precambrian shields.

Uses & applications

Extensively used in construction for countertops, floor tiles, and monument stone. Also used for curbing and crushed stone in infrastructure projects.

Geological facts

Granite is the most common igneous rock found in Earth's continental crust. Mount Rushmore is carved into a massive granite batholith. It is resistant to acid rain and highly durable.

Field identification & locations

Identify by its 'salt and pepper' appearance and visible interlocking crystals. Common in mountain ranges and glacial erratic deposits. Collectors look for unique color variations or large phenocrysts (Porphyritic granite).

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