igneous

Peridotite (with Olivine)

Peridotite (rich in Olivine, (Mg,Fe)2SiO4)

Hardness: 6.5-7 (olivine); Color: Olive-green to lime-green crystals in a dark grey or black matrix; Luster: Vitreous to oily; Crystal structure: Orthorhombic; Specific Gravity: 3.2-3.4.

Hardness: 6
Luster: Vitreous to oily

Identified April 6, 2026More igneous →

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Physical properties

Hardness: 6.5-7 (olivine); Color: Olive-green to lime-green crystals in a dark grey or black matrix; Luster: Vitreous to oily; Crystal structure: Orthorhombic; Specific Gravity: 3.2-3.4.

Formation & geological history

Formed deep within the Earth's mantle through fractional crystallization of magma. These specimens are often brought to the surface as xenoliths inside basaltic lava flows during volcanic eruptions.

Uses & applications

Primary source of the gemstone Peridot; used in industrial refractory processes due to high melting points; significant for geological research on mantle composition.

Geological facts

Peridotite is the dominant rock of the upper part of Earth's mantle. Common green olivine crystals found within it are often called 'Hawaiian diamonds' when found in volcanic sands.

Field identification & locations

Identify in the field by looking for distinct yellowish-green glassy crystals embedded within dark, heavy, fine-grained volcanic rock (basalt). Common in volcanic regions like Hawaii, Arizona, and the Canary Islands.

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