igneous

Granite

Phaneritic plutonic rock (SiO2 > 69%)

Hardness: 6-7 on Mohs scale; Color: Gray, salt-and-pepper, with reddish-brown oxidation; Luster: Dull to vitreous; Crystal structure: Phaneritic (medium-grained); Cleavage: Indistinct; Specific gravity: 2.63-2.75.

Hardness: 6-7 on Mohs scale
Color: Gray, salt-and-pepper, with reddish-brown oxidation
Luster: Dull to vitreous

Identified May 28, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow crystallization of silica-rich magma beneath the Earth's surface. This specimen appears weathered and oxidized, representative of continental crust formations often millions of years old.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, and monuments due to its durability and aesthetic appeal.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in the Black Hills of South Dakota.

Field identification & locations

Identify in the field by checking for a visible interlocking crystalline texture of quartz and feldspar and a high resistance to scratching. Common in mountainous regions or areas with exposed glacial till.

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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