Peridot
Peridot
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Peridot

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Peridot

Peridot (/ˈpɛrɪˌdɒt/ PERR-ih-dot), sometimes called chrysolite, is a yellow-green transparent variety of olivine. Peridot is one of the few gemstones that occur in only one color.

Peridot can be found in mafic and ultramafic rocks occurring in lava and peridotite xenoliths of the mantle. The gem occurs in silica-deficient rocks such as volcanic basalt and pallasitic meteorites. Along with diamonds, peridot is one of only two gems observed to be formed not in Earth's crust, but in the molten rock of the upper mantle. Gem-quality peridot is rare on Earth's surface due to its susceptibility to alteration during its movement from deep within the mantle and weathering at the surface. Peridot has a chemical formula of (Mg,Fe)2SiO4.

Peridot is one of the birthstones for the month of August.

The origin of the name peridot is uncertain. The Oxford English Dictionary suggests an alteration of AngloNorman pedoretés (classical Latin pæderot-), a kind of opal, rather than the Arabic word faridat, meaning "gemstone".

The Middle English Dictionary's entry on peridot includes several variations: peridod, peritot, pelidod and pilidod — other variants substitute y for letter i used here.

The earliest use of the word in English is possibly in the 1705 register of the St. Albans Abbey: The dual entry is in Latin with the translation to English listed as peridot. It records that on his death in 1245, Bishop John bequeathed various items, including peridot gems, to the Abbey.

Peridot is one of the few gemstones that occur in only one color: an olive-green. The intensity and tint of the green, however, depends on the percentage of iron in the crystal structure, so the color of individual peridot gems can vary from yellow, to olive, to brownish-green. In rare cases, peridot may have a medium-dark toned, pure green with no secondary yellow hue or brown mask. Lighter-colored gems are due to lower iron concentrations.

The molecular structure of peridot consists of isomorphic olivine, silicate, magnesium and iron in an orthorhombic crystal system. In an alternative view, the atomic structure can be described as a hexagonal, close-packed array of oxygen ions with half of the octahedral sites occupied by magnesium or iron ions and one-eighth of the tetrahedral sites occupied by silicon ions.

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