Igneous

Granite

Granite (Silicic Intrusive Igneous Rock)

Hardness (Mohs): 6-7; Color: Mottled gray, white, and black; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained) featuring quartz, feldspar, and mica; Cleavage: None (fractures irregularly); Specific gravity: 2.63 to 2.75

Color: Mottled gray, white, and black
Luster: Vitreous to dull

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow subterranean cooling and crystallization of magma deep within the Earth's crust (plutonic). They are found in continental crust across all geological ages, notably in mountain-building belts.

Uses & applications

Widely used in construction for countertops, floor tiles, paving stones, and monuments; also used as crushed stone for road base and railroad ballast.

Geological facts

Granite makes up a significant portion of the Earth's continental crust. Iconic landforms like Yosemite's El Capitan and Mount Rushmore are made entirely of granite.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals. It is found globally in large batholiths. Collectors should look for sharp crystal boundaries and a lack of layering to distinguish it from gneiss.

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