igneous

Granite

Phaneritic Felsic Igneous Rock

Hardness: 6-7 on Mohs scale; Color: Pink, white, gray, and black mottled appearance; Luster: Dull to vitreous (glassy); Crystal Structure: Phaneritic (coarse-grained) consisting mainly of quartz, K-feldspar, and plagioclase; Cleavage: None (fractures irregularly); Specific Gravity: 2.63 to 2.75.

Hardness: 6-7 on Mohs scale
Color: Pink, white, gray, and black mottled appearance
Luster: Dull to vitreous (glassy)

Identified March 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of silica-rich magma beneath the Earth's surface (intrusive). Most granite plutons date from the Precambrian to Cenozoic eras, often associated with continental crust formation and mountain-building events.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stone, and curbing. It is also used for monuments, gravestones, and as an aggregate in road construction. High-quality specimens with unique patterns are sought after by hobbyist collectors for tumbling.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a granite batholith. Because it is so hard and durable, it was the preferred building material for many ancient Egyptian pyramids and temples.

Field identification & locations

Identify in the field by its 'salt and pepper' or mottled look and visible interlocking crystals. You can find it in continental mountain ranges or as glacial erratics in gravel pits. It will not be scratched by a steel knife and will not fizz with acid.

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