igneous

Granite

Granite (composed primarily of Quartz SiO2, Alkali Feldspar (K,Na)AlSi3O8, and Plagioclase Feldspar)

Hardness: 6-7 on Mohs scale; Color: Mottled pink, gray, white, and black; Luster: Vitreous to dull; Structure: Phaneritic (coarse-grained) crystalline; Cleavage: None (though feldspars within show cleavage); Specific Gravity: 2.63 to 2.75

Hardness: 6-7 on Mohs scale
Color: Mottled pink, gray, white, and black
Luster: Vitreous to dull

Identified March 18, 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). The large visible crystals indicate a long cooling process. Ages range from Archean to recent, depending on the specific pluton.

Uses & applications

Extensively used in construction for countertops, floor tiles, and paving stones. Also used in monuments, curbing, and as aggregate for roads. Occasional use in jewelry as polished 'granite jasper' or tumbled stones.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Famous landmarks like Mount Rushmore and Yosemite's El Capitan are carved into or composed of granite. It is extremely durable and resistant to acid rain.

Field identification & locations

Identify by its 'salt and pepper' look with visible, interlocking crystals of different colors. It will not be scratched by a steel knife. Commonly found in mountainous regions or areas where ancient crust is exposed (shields). Look for the mix of translucent quartz and opaque pink or white feldspar.

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