igneous

Granite

Granite (Alkali feldspar, Plagioclase feldspar, and Quartz)

Hardness: 6-7 (Mohs). Color: Pinkish-gray mottled with white and black translucent grains. Luster: Dull to vitreous. Crystal structure: Phaneritic (coarsegrained holocrystalline). Cleavage: Poor; fractures irregularly. Specific Gravity: 2.63 - 2.75.

Hardness: 6-7 (Mohs)
Color: Pinkish-gray mottled with white and black translucent grains
Luster: Dull to vitreous

Identified March 30, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of magma below Earth's surface (intrusive). Most granite dates back to the Precambrian or Paleozoic eras. It forms the core of many mountain ranges and stable continental cratons.

Uses & applications

Extensively used in construction for dimensional stone, countertops, monuments, and paving. Crushed granite is used as an aggregate in road construction and concrete.

Geological facts

Granite makes up the majority of the Earth's continental crust. Mount Rushmore is carved into a granite batholith. It is one of the hardest and most durable common natural stones used by humans.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible, interlocking mineral crystals (quartz, feldspar, mica). Commonly found in mountainous regions or areas with exposed glacial till. To collect, look for unweathered surfaces showing clear grain boundaries.

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