Peridot Physical Properties

Peridot Physical Properties loose sale price & Apple Green Peridot Gemstone Information

Peridot (pronounced pair-a-doe) is the gem variety of olivine. Olivine, which is actually not an official mineral, is composed of two minerals: fayalite and forsterite. Fayalite is the iron rich member with a pure formula of Fe2SiO4. Forsterite is the magnesium rich member with a pure formula of Mg2SiO4. Olivine's formula is written as (Mg, Fe)2SiO4 to show the substitution of the magnesium and iron. Peridot is usually closer to forsterite than fayalite in composition although iron is the coloring agent for peridot. The best colored peridot has an iron percentage of less than 15% and includes nickel and chromium as trace elements that may also contribute to the best peridot color.

• Peridot Chemical composition: (MgFe)2SiO4
• Class: nesosilicate
• Crystal system: orthorhombic; 2/m2/m2/m
• Crystal habit: commonly as compact or granular masses, also as loose or embedded grains, sometimes in volcanic nodules. Crystals are rare, usually as vertically striated prisms.
• Twinning: twinning is uncommon, simple twinning can occur on {100}, {011}, and {012}. Cyclic twinning on {031} reportedly produces trillings.
• Specific gravity: 3.22 - 3.45, increases with iron content
• Index of refraction: 1.65 - 1.69, increases with iron content
• Birefringence: strong, (0.035 - 0.038)
• Pleochroism: weak; pale yellow-green to yellow/pale yellow-green to yellow/yellow to yellow orange
• Hardness: 6.5 to 7, hardness increases with magnesium content
• Color: olive green, green, yellow, brown
• Luster: vitreous to oily
• Transparency: transparent to translucent
• Cleavage: poor on {010} and {110}, {010} cleavage improves with increasing iron content
• Fracture: conchoidal
• Streak: colorless