Peridot (Olivine in Basalt)
Olivine var. Peridot · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Orthorhombic; typically occurs as rounded grains or granular masses in volcanic rock, rarely as distinct tabular crystals.
Mineral Group
Silicates (Nesosilicate)
Chemical Formula
(Mg, Fe)2SiO4 (Magnesium Iron Silicate)
Formation Process
Igneous; crystallizes deep within the Earth's mantle and is carried to the surface by basaltic magmas. It forms under high temperature and pressure conditions.
About This Crystal
Small, olive-green to yellowish-green granular crystals embedded within a dark, fine-grained volcanic matrix (basalt). The crystals show a glassy luster and are translucent to transparent.
Physical Characteristics
Color: Olive-green, lime-green; Streak: Colorless/White; Cleavage: Poor; Fracture: Conchoidal; Specific Gravity: 3.27–4.37; Luster: Vitreous; Fluorescence: None.
Optical Properties
Biaxial positive; Refractive Index: 1.654–1.690; Birefringence: 0.035–0.038; Strong pleochroism is usually absent in pale specimens; Doubly refractive.
Hardness & Durability
Origin Region
Arizona (San Carlos Reservation), Hawaii, Canary Islands, and Pakistan. Often found in mafic and ultramafic volcanic rocks like Basalt.
Hardness & Durability
Mohs Hardness: 6.5 to 7. Brittle tenacity; Fair to good toughness but sensitive to thermal shock and rapid temperature changes.
Care & Maintenance
Clean with warm soapy water only. Avoid ultrasonic cleaners, steam cleaners, and harsh acids. Store away from harder gems like sapphire or diamond to prevent scratching.
Rarity & Value
Common as a mineral (Olivine), but gem-quality (Peridot) is more restricted. Small grains in basalt are common; large, clear crystals are rare and valuable.
Special Characteristics
Contains high magnesium content. In volcanic xenoliths like this, it often shows 'lily pad' inclusions when faceted, though here it appears as a raw mineral aggregate.
Lore & History
Historically known as 'the gem of the sun' by ancient Egyptians. It is the birthstone for August and has been used for millennia in protective amulets and jewelry.