perdotos

Perdotos are the gem-quality variety of the mineral olivine, a magnesium-iron silicate with the general formula (Mg,Fe)2SiO4. They represent the solid solution between forsterite and fayalite, typically magnesium-rich, and their color ranges from olive green to yellow-green, driven mainly by iron content. Perdotos are usually transparent to translucent with a glassy luster and rate about 6.5–7 on the Mohs scale. They have little to no cleavage and tend to fracture conchoidally or irregularly.

Geologically, perdotos form in high-temperature settings. They occur in mafic and ultramafic igneous rocks, particularly basaltic magmas, and in mantle-derived xenoliths carried to the surface by volcanic activity. They are also found in meteorites, notably pallasites, where olivine crystals coexist with nickel-iron.

Prominent modern sources include the San Carlos Reservation in Arizona, USA, and Zabargad (St. John’s Island) in the Red Sea. Other notable producers are Pakistan, Myanmar, China, Tanzania, and Russia. In jewelry, perdotos are cut into cabochons or faceted to maximize color; heat treatment is uncommon but may be used to improve color in some stones. Perdotos have been valued since antiquity for their distinctive green hue and remain a popular gemstone in contemporary jewelry.