Igneous

Granite

Granite (composed primarily of Quartz SiO2, Potassium Feldspar KAlSi3O8, and Plagioclase)

Hardness: 6-7 on Mohs scale. Color: Mottled pink, white, and grey. Luster: Vitreous to pearly. Crystal structure: Phaneritic (coarse-grained visible crystals). Cleavage: Varies by mineral constituent; no overall cleavage. Specific gravity: 2.63 to 2.75.

Hardness: 6-7 on Mohs scale
Color: Mottled pink, white, and grey
Luster: Vitreous to pearly

Identified March 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling and crystallization of silica-rich magma deep within the Earth's crust (plutonic). Found in continental crust ranging from the Archean Eon to the Cenozoic Era.

Uses & applications

Extensively used in construction for countertops, floor tiles, and paving stones. Also used in monuments, curbing, and as crushed stone for road base and railway ballast.

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 of its hardness, it was used by ancient Egyptians for sarcophagi and obelisks.

Field identification & locations

Identify by its 'salt and pepper' appearance and visible interlocking crystals of different colors. Commonly found in mountain ranges (orogenic belts) and glacial deposits. Collectors look for unique vein patterns or large phenocrysts (porphyritic texture).

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