Olivine
Olivine is a common silicate mineral that ranges in composition from forsterite (Mg2SiO4) to fayalite (Fe2SiO4). This solid solution series is part of the nesosilicate group, where the silica tetrahedra are isolated from each other, making olivine a magnesium iron silicate with the formula (Mg,Fe)2SiO4.
Properties
- Color: Olivine can vary from olive green to yellow-green, depending on its iron content; higher iron content makes it darker.
- Crystal System: Orthorhombic.
- Hardness: 6.5 to 7 on the Mohs scale.
- Luster: Vitreous (glassy).
- Cleavage: Poor cleavage on {010}, {001}, and {110}.
- Fracture: Conchoidal.
- Streak: White or colorless.
- Density: 3.27 to 3.37 g/cm3, increasing with iron content.
Formation and Occurrence
Olivine forms at high temperatures and is commonly found in:
- Mantle rocks, where it is one of the primary minerals in the Earth's upper mantle.
- Peridotite and Dunite, which are ultramafic igneous rocks.
- Basaltic lavas, especially in Kimberlite pipes, which are often associated with diamond deposits.
Olivine is not stable at Earth's surface conditions and will weather to form serpentine, iddingsite, or other secondary minerals.
Historical Context
The name "olivine" derives from its olive-green color, first used in the late 18th century. Its mineralogical properties were well studied by mineralogists in the 19th century, with its importance in geology and petrology becoming increasingly recognized. Olivine's use as a gemstone, known as Peridot, dates back to ancient Egypt, where it was called the "gem of the sun."
Applications
- Gemstone: When of gem quality, olivine is known as peridot, a popular gemstone valued for its bright green color.
- Industrial Uses: Olivine sand is used for foundry sand, abrasive blasting, and as a refractory material due to its high melting point.
- Carbon Sequestration: Olivine can be used in enhanced weathering techniques to capture CO2 from the atmosphere through mineral carbonation.
Notable Locations
Olivine occurs worldwide, with significant deposits in:
- San Carlos, Arizona, USA, where it is extracted from Xenoliths in basalt.
- Norway, where it's found in peridotites.
- Hawaii, where olivine crystals are often found in basaltic rocks.
- Myanmar, known for producing high-quality peridot.
Sources
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