igneous
Olivine in Basalt (Peridot)
Magnesium Iron Silicate (Mg, Fe)2SiO4 in Vesicular Basalt
Hardness: 6.5–7 Mohs; Color: Olive green to lime green crystals in a dark grey/black matrix; Luster: Vitreous (glassy); Crystal Structure: Orthorhombic; Cleavage: Poor; Specific Gravity: 3.2–4.3 for the mineral.
- Hardness
- 6
- Luster
- Vitreous (glassy)
Identified More igneous →
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Physical properties
Hardness: 6.5–7 Mohs; Color: Olive green to lime green crystals in a dark grey/black matrix; Luster: Vitreous (glassy); Crystal Structure: Orthorhombic; Cleavage: Poor; Specific Gravity: 3.2–4.3 for the mineral.
Formation & geological history
Formed deep within the Earth's mantle and brought to the surface via volcanic eruptions. The green crystals (phenocrysts) cooled slowly underground, while the surrounding basalt (the dark rock) cooled more rapidly at the surface. These specimens are found in volcanic regions of all ages, from Cenozoic to Precambrian.
Uses & applications
Larger, cleaner crystals are cut into 'Peridot' gemstones for jewelry. In industry, olivine is used as a refractory material in steel making (high melting point) and as a replacement for silica sand in sandblasting.
Geological facts
Olivine is a major component of the Earth's upper mantle and has also been identified in meteorites (pallasites) and on the surface of Mars and the Moon. It's often one of the first minerals to crystallize from a cooling magma.
Field identification & locations
Identify in the field by the distinctive 'bottle glass' green color contrasting against dark, heavy volcanic rock. Commonly found in Arizona (Peridot Mesa), Hawaii, Norway, and Iceland. Collectors should look for vibrant color and transparency.
