Igneous

Granite

Granite (Felsic Plutonic Rock)

Hardness: 6-7 (Mohs scale); Color: Salt-and-pepper (combination of white, grey, black, and sometimes pink); Luster: Phaneritic (visible crystals), vitreous to dull; Crystal structure: Coarse-grained granular; Cleavage: None (fractures irregularly); Specific gravity: 2.63 - 2.75

Hardness: 6-7 (Mohs scale)
Luster: Phaneritic (visible crystals), vitreous to dull

Identified March 16, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of magma below Earth's surface (intrusive). The coarseness of the grains indicates it cooled very slowly over thousands of years. It can date from the Archean Eon to the Cenozoic Era, commonly appearing in the continental crust.

Uses & applications

Used extensively in construction for dimension stone, countertops, floor tiles, and paving. It is also utilized in heavy engineering as aggregate for road base and railroad ballast. Small polished specimens are common in beginner rock collections.

Geological facts

Granite is the primary component of Earth's continental crust and is unique to Earth among the planets in our solar system. Mount Rushmore and Yosemite's Half Dome are famous landmarks carved from granite plutons.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and interlocking visible crystals of quartz (clear/grey) and feldspar (white/pink). Found frequently in glaciated areas as 'glacial erratics' or in mountain ranges. It is very resistant to weathering.

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