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Peridot is gem-quality olivine colored in green color of different intensity, most often with a yellowish hue. Peridot is the fayalitic minal variety of olivine according to mineralogical classification with the "forsterite-fayalite" within the range of 10-30% (olivine itself in foreign literature). Peridot is the gem variety of the mineral olivine in English-speaking countries. This name was registered at the CIBJO congress in 1968. The name "peridot" comes from the ancient Greek - "χρυσός" - "gold" and "λίθος" - "stone" (golden stone).
Crystal system: Rhombic, Rhombo-dipyramidal crystal class (point symmetry group);
Color: Peridot crustal structure includes iron and iron Fe2+ is the cause of its attractive yellowish green colors, and yellow and brown colors are associated with an isomorphic admixture of iron Fe3+. Also peridot may vary in colors due to the isomorphous impurities Cr3+ and/or V3+.
|Mohs hardness:||6.5 – 7|
|Density:||3.28 – 3.48 g/cm3|
|Cleavage:||imperfect to medium on (010), imperfect on (100)|
|Optical character:||anisotropic, biaxial (from negative to positive)|
|Refractive Index:||np =1.650 – 1.693, nm =1.671 – 1.716, ng =1.686 – 1.731|
|Birefringence:||0.036 – 0.038|
Inclusions and structural inhomogeneities
Gem basic treatments
|Heat treatment||Lightening or improving the green hue|
|Impregnation with various coloring compounds||Altering the gem visual color|
|Surface coating by applying a various coloring agent||Altering the gem visual color|
Synthetic or Imitation gem materials
Synthetic peridot for the jewelry industry is not produced. A wide application of synthetic olivine finds in metallurgy and the industry of heat-resistant materials. However, cases of the use of synthetic olivines and olivines from technogenic slags are known. From synthetic olivine, entering the jewelry market, forsterite is known - colorless and blue-violet (often used for tanzanite imitation).
As imitations of peridot are used as follows:
- synthetic minerals with a similar color (fianit, garnets, spinel, corundum);
- doublets and triplets: glass + natural or synthetic olivine;
- color glass;