igneous

Granite

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

Hardness: 6-7 Mohs; Color: Pinkish-grey with black speckles (biotite/hornblende); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: None in the rock itself, though mineral components may show it; Specific gravity: 2.63 to 2.75.

Hardness: 6-7 Mohs
Color: Pinkish-grey with black speckles (biotite/hornblende)
Luster: Vitreous to dull

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of magma below Earth's surface (intrusive). Geological age varies from Precambrian to Cenozoic. It forms the core of many mountain ranges and continental crust.

Uses & applications

Major use in construction (countertops, floor tiles, paving stones), dimension stone for monuments and curbing, and crushed stone for road base or railroad ballast.

Geological facts

Mount Rushmore is carved into a massive granite batholith in South Dakota. Granite is one of the hardest and most durable common stones, which is why it has been used for thousands of years in architecture, including Ancient Egyptian pyramids.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible, interlocking crystals of quartz, feldspar, and dark mica. It is found globally in continental shields. Collectors look for unique mineral inclusions like tourmaline or large feldspar phenocrysts.

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