igneous

Anorthosite

Anorthosite (dominated by Plagioclase Feldspar)

Hardness: 6-6.5 (Mohs scale); Color: light grey to medium grey, often with bluish or greenish tints; Luster: Pearly to vitreous; Crystal Structure: Triclinic; Cleavage: Perfect in two directions; Specific Gravity: 2.62-2.76.

Hardness: 6-6
Luster: Pearly to vitreous

Identified April 3, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of magma deep beneath the Earth's crust (plutonic). It is characterized by the accumulation of plagioclase crystals in a magma chamber. These rocks are often ancient, dating back to the Proterozoic eon (over 1 billion years ago).

Uses & applications

Used primarily as decorative stone (countertops, memorials), dimension stone in construction, or crushed for railroad ballast. High-quality iridescent varieties (Labradorite) are used in jewelry.

Geological facts

Anorthosite makes up the majority of the light-colored 'highlands' on the Earth's moon. It is far more common on the Moon than on the Earth's surface.

Field identification & locations

Identify in the field by its light-to-medium grey color and the prevalence of large, shiny cleavage surfaces of feldspar crystals. Often found in large massifs like the Adirondack Mountains or the Canadian Shield.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral