igneous

Peridot in Basalt/Xenolith

Olivine (Mg, Fe)2SiO4 in Vesicular Basalt

Hardness: 6.5-7 (Olivine), 5-6 (Basalt); Color: Olive green to lime green crystals within a dark grey or black matrix; Luster: Vitreous (glassy) for the crystals, dull/earthy for the matrix; Structure: Orthorhombic crystals appearing as granular masses; Specific Gravity: 3.2-4.4.

Hardness: 6

Identified March 28, 2026More igneous →

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Physical properties

Formation & geological history

Formed deep within the Earth's upper mantle and brought to the surface via volcanic eruptions. The green olivine crystals (xenoliths) were trapped in the basaltic lava as it cooled rapidly on or near the surface. Most are from the Cenozoic era or younger.

Uses & applications

Larger, clear crystals are faceted into Peridot jewelry (August birthstone). Smaller specimens are common in geological collecting and education. Basalt itself is used extensively in construction and road aggregate.

Geological facts

Olivine is one of the first minerals to crystallize from magma. Large pockets of these crystals are found in the San Carlos Apache Reservation in Arizona, which provides much of the world's gem-quality peridot. Examples have also been found in meteorites known as pallasites.

Field identification & locations

Identify by looking for glassy, olive-green granular aggregates embedded in a fine-grained, dark, often holy (vesicular) volcanic rock. Common in Hawaii, Arizona, and volcanic regions of New Mexico and Canary Islands. Collectors should look for vibrant green color and high clarity in the crystals.

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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)

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Blue Apatite

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

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Magnetite

Magnetite (Fe3O4)

mineral