Igneous

Granite

Granite (Phaneritic intrusive igneous rock)

Hardness: 6-7 on Mohs scale; Color: Variable (white, grey, pink with dark mottling); Luster: Vitreous to dull; Crystal structure: Coarse-grained (phaneritic); Cleavage: Indistinct; Specific gravity: 2.65-2.75.

Hardness: 6-7 on Mohs scale
Color: Variable (white, grey, pink with dark mottling)
Luster: Vitreous to dull

Identified March 27, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface. Most granite dates back to the Precambrian or Paleozoic eras, though it forms whenever continental crust undergoes melting.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments because of its durability and aesthetic appeal.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Its name comes from the Latin 'granum', meaning a grain, in reference to its coarse-grained structure. Mount Rushmore is carved into a granite batholith.

Field identification & locations

Identify in the field by its visible interlocking crystals of quartz (clear/grey), feldspar (white/pink), and mica (black/shiny). Extremely common in mountain ranges and continental shields. Collectors look for unique mineral inclusions or rare colors.

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