igneous

Granite (Alkali-feldspar Granite)

Felsic Plutonic Rock (Primary minerals: Quartz SiO2, Orthoclase KAlSi3O8, Plagioclase (Na,Ca)AlSi3O8)

Hardness: 6-7 Mohs; Color: Pinkish-red, white/clear, and dark grey; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained/visible crystals); Cleavage: None in quartz, perfect in feldspar; Specific gravity: 2.63 - 2.75

Hardness: 6-7 Mohs
Color: Pinkish-red, white/clear, and dark grey
Luster: Vitreous to dull

Identified March 8, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling and crystallization of silica-rich magma deep within the Earth's crust (plutonic). Found in continental tectonic plates; often Proterozoic or Paleozoic in age for surface exposures.

Uses & applications

Used extensively in construction for countertops, floor tiles, and gravel. It is also a popular material for monuments, sculptures, and as a decorative landscaping stone.

Geological facts

Granite makes up the majority of Earth's continental crust. Mount Rushmore is carved into a giant granite formation in the Black Hills. Pink hues are specifically caused by high concentrations of potassium feldspar (orthoclase).

Field identification & locations

Identify in the field by looking for a 'salt and pepper' or interlocking crystalline texture where common minerals like quartz and feldspar are visible to the naked eye. Found in mountain ranges and glacial deposits worldwide.

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