igneous

Olivine in Basalt (Peridotite Xenolith)

Forsterite-rich Olivine (Mg2SiO4) in Aphanitic Basalt

Hardness: 6.5-7 (Olivine), 5-6 (Basalt matrix); Color: Olive-green to lime-green phenocrysts in a grey/brown weathered matrix; Luster: Vitreous (glassy) on crystals; Crystal Structure: Orthorhombic; Specific Gravity: ~3.3

Hardness: 6
Luster: Vitreous (glassy) on crystals

Identified March 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed deep within the Earth's upper mantle or in magnesium-rich magma chambers. These specimens often represent 'xenoliths' (foreign rocks) brought to the surface by rapid volcanic eruptions of basaltic lava. Geological age varies by locality but typically ranges from Cenozoic to recent volcanic activity.

Uses & applications

Primary source of the gemstone Peridot; used in industry for refractory sand and casting, and as a geological indicator of mantle processes.

Geological facts

Olivine is one of the first minerals to crystallize from a cooling magma. It is also found in stony-iron meteorites known as Pallasites, making it a mineral of extraterrestrial significance.

Field identification & locations

Identify by looking for glassy green 'pockets' or crystals embedded in a dark, fine-grained volcanic rock. Commonly found in volcanic fields such as those in Arizona (Peridot Mesa), Hawaii, and various locations in Norway and China.

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