Name/Title
Olivine var. PeridotEntry/Object ID
2009.62.209Description
Description: Chemistry: (Mg, Fe)2SiO4, Magnesium Iron Silicate.
Class: Silicates
Subclass: Nesosilicates
Group: Olivine
PHYSICAL CHARACTERISTICS:
Color is a light near emerald green to the more common pale yellowish green; also found colorless, greenish brown to black. A near colorless specimen is likely nearly pure forsterite, while a greenish-brown to black specimen may approach pure fayalite in composition. Anything in-between is olivine.
Luster is vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System is orthorhombic; 2/m 2/m 2/m.
Crystal Habits include flatten tabular to box shaped crystals, but good crystals are rare. More commonly found as grains in alluvial gravels and as granular xenoliths in magnesium rich volcanic rock. Also massive. Twinning is rare, but has produced star shaped trillings.
Cleavage is poor in two directions at 90 degrees, is more distinct in fayalite.
Fracture is conchoidal.
Hardness is 6.5 - 7.
Specific Gravity is approximately 3.2 for forsterite - 4.3 for fayalite (above average for non-metallic minerals).
Streak is white.
Other Characteristics: Index of refraction is 1.64 - 1.70 and has double refraction.
Associated Minerals are diopside, spinel, plagioclase feldspars, chromite, hornblende, serpentine, iron-nickel meteorites and augite.
Best Field Indicators are color, hardness, mafic igneous or metamorphic environment of formation, lack of good cleavage and density.
Occurrence: Notable Occurrences are numerous and include the ancient source of Zagbargad Island in the Red Sea off the coast of Egypt; Mogok, Myanmar (formerly known as Burma); South Africa; Ural Mountains, Russia; Kohistan, Pakistan; Norway; Sweden; France; Minas Gerais, Brazil; Eifel, Germany; Chihuahua, Mexico; Ethiopia; Victoria, Australia; China and Salt Lake Crater, Oahu, Hawaii; North Carolina; New Mexico and Peridot Mesa, San Carlos Apache Reservation, Gila County, Arizona, USA.
Variety: Olivine's gemstone variety, known as peridot, is one of the most mispronounced of gemstone names. The correct pronunciation has peridot rhyming with doe or depot. But peridot is often pronounced incorrectly so that it rhymes with dot. Peridot is the birthstone of August and is usually a very affordable colored gemstone. Unfortunately it is often compared to the rich dark green of emerald and in this comparison it is often found lacking. But peridot has its own unique green-yellow color that is different from emerald and this comparison is rather unfair. Most peridot is actually the magnesium rich forsterite and its color is caused by the presence of iron ions. Fayalite's higher iron content make for darker, less attractive specimens that are not generally used as gemstones. The best colored peridot has an iron percentage less than 15% and includes nickel and chromium as trace elements that may also contribute to the best peridot color. Peridot is a colorful, affordable and attractive gemstone.Collection
RAGM Mineral CollectionAcquisition
Accession
2009.62Source or Donor
Museum Collection of MineralsAcquisition Method
DonationLocation
Category
PermanentMoved By
Ian CunninghamDate
May 31, 2024
