igneous

Granite

Granite (Silicic Plutonic Rock)

Hardness: 6-7 Mohs; Color: Gray, salt-and-pepper, white; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Perfect on feldspar grains, none on quartz grains; Specific Gravity: 2.63 - 2.75.

Hardness: 6-7 Mohs
Color: Gray, salt-and-pepper, white
Luster: Vitreous to dull

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling and crystallization of magma deep underground (plutonic). Found in continental crust; typical age ranges from Precambrian to Cenozoic.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments. It is also used as crushed stone for road base.

Geological facts

Granite makes up the core of most mountain ranges. Mount Rushmore is carved into a massive granite batholith in South Dakota. It is one of the hardest and most durable natural stones.

Field identification & locations

Identify in the field by its 'salt and pepper' look with visible interlocking crystals of quartz (clear/gray), feldspar (white/pink), and mica (black flakes). Commonly found in mountainous regions or shield areas like the Canadian Shield.

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