igneous

Granite

Phaneritic intrusive igneous rock (composed mainly of Quartz SiO2, Feldspar KAlSi3O8, and Biotite/Mica)

Hardness: 6-7 Mohs; Color: Salt and pepper appearance with pink, white, and dark grey/black flecks; Luster: Vitreous to pearly; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Perfect on feldspar grains, none on quartz.

Hardness: 6-7 Mohs
Luster: Vitreous to pearly

Identified January 12, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface. It is a plutonic rock that cools over thousands of years, allowing large crystals to grow. Most granite dates from the Precambrian to Cenozoic eras.

Uses & applications

Extensively used in construction for countertops, flooring, curbing, and monuments. It is also used as crushed stone for road base and railroad ballast due to its high durability and strength.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in South Dakota. It is one of the hardest and most common rocks on the planet.

Field identification & locations

Identify by looking for intergrown visible crystals of quartz (glassy), feldspar (opaque white/pink), and mica (shiny black flakes). Found globally in mountain ranges and continental shields like the Canadian Shield or the Appalachians.

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