igneous

Granite

Granite (Phaneritic intrusive igneous rock) - Composition: SiO2, Al2O3, K2O, Na2O

Hardness: 6-7 on Mohs scale; Color: Pink, white, gray, and black speckles; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Distinct in feldspar minerals, none in quartz; Specific gravity: 2.63 to 2.75

Hardness: 6-7 on Mohs scale
Color: Pink, white, gray, and black speckles
Luster: Vitreous to dull

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 (plutonic). Found in continental crust, often dating from the Precambrian to Cenozoic eras, typically in mountain belts or cratons.

Uses & applications

Extensively used in construction for countertops, floor tiles, curbing, and gravestones. Also used as crushed stone (aggregate) for road base and railroad ballast.

Geological facts

Granite makes up the core of most continents. It is one of the hardest natural stones, which is why it's a preferred material for monuments that are meant to last centuries. Mount Rushmore is carved into a granite batholith.

Field identification & locations

Identify in the field by its 'salt and pepper' look with visible mineral grains of quartz (translucent), feldspar (opaque white/pink), and mica (shiny black flakes). Common in mountainous regions like the Sierra Nevada or 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