igneous

Granite

Phaneritic Igneous Rock (composed primarily of Quartz, Alkali Feldspar, and Plagioclase)

Hardness: 6-7 on Mohs scale; Color: typically white, pink, or gray with dark specks; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: None (though feldspar components have cleavage); Specific Gravity: 2.63 to 2.75

Hardness: 6-7 on Mohs scale
Color: typically white, pink, or gray with dark specks
Luster: Vitreous to dull

Identified March 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow crystallization of magma below Earth's surface (intrusive). The process can take millions of years, and these rocks are found in continental crust across all geological ages, notably in mountain-building belts.

Uses & applications

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

Geological facts

Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a granite batholith, and some of the oldest known rocks on Earth are granitic gneisses dating back over 4 billion years.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals. It is found globally in mountain ranges and shield areas. Collectors look for unique mineral inclusions like tourmaline or large feldspar phenocrysts.

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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral