igneous

Granite

Granitoid (composition typically SiO2, Al2O3, K2O, Na2O)

Hardness: 6-7 on Mohs scale; Color: typically white, pink, or gray with darker specks; Luster: dull to vitreous; Crystal structure: phaneritic (large, visible grains); Cleavage: none (fractures irregularly); Specific gravity: 2.63 - 2.75

Hardness: 6-7 on Mohs scale
Color: typically white, pink, or gray with darker specks
Luster: dull to vitreous

Identified March 25, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of magma below Earth's surface (intrusive). The process can take millions of years and occurs primarily during the Archean to Cenozoic eras in continental crust/mountain building zones.

Uses & applications

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

Geological facts

Granite makes up a large portion of the Earth's continental crust. It is one of the hardest substances in the world, second only to diamonds. Mount Rushmore is carved into a massive granite batholith in South Dakota.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals of quartz, feldspar, and mica. Found globally in continental mountain ranges and shield areas. Collectors look for unique mineral inclusions like tourmaline or garnet.

Other igneous specimens

See all

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