Peridot in Basalt
Olivine var. Peridot · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Orthorhombic; typically occurs as rounded grains or stubby prismatic crystals within the host matrix.
Mineral Group
Silicates (Nesosilicate)
Chemical Formula
(Mg, Fe)2SiO4
Formation Process
Igneous; forms deep in the Earth's mantle and is brought to the surface as xenoliths within basaltic lava flows.
About This Crystal
The specimen features translucent to opaque, olive-green to yellowish-green crystals embedded in a dull, grey, fine-grained basaltic matrix. The luster is vitreous on fresh surfaces but can appear waxy or dull in weathered matrix-bound specimens.
Physical Characteristics
Color: Olive-green; Streak: Colorless/White; Cleavage: Poor; Fracture: Conchoidal; Specific Gravity: 3.27–3.37; Fluorescence: Non-fluorescent.
Optical Properties
Biaxial positive; Refractive Index: 1.654–1.690; Strong birefringence (0.036); No significant pleochroism in these small grains.
Hardness & Durability
Origin Region
Arizona (San Carlos Apache Reservation), Hawaii, Canary Islands, or Pakistan. Typically found in ultramafic igneous rocks.
Hardness & Durability
Mohs hardness: 6.5–7; Toughness: Fair to Good; Stability: Sensitive to rapid temperature changes and some acids.
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid ultrasonic cleaners, steam cleaners, and harsh household chemicals.
Rarity & Value
Common as small grains in basalt (olivine sand), but gem-quality Peridot over 5 carats is uncommon and more valuable. Matrix specimens are valued as mineralogical teaching tools.
Special Characteristics
The visible green crystals are xenocrysts—crystals that formed in the mantle and were trapped in the rising magma.
Lore & History
Known as the 'Gem of the Sun' by ancient Egyptians; historically mined on St. John's Island (Zabargad) in the Red Sea. Traditionally associated with the Heart Chakra and believed to promote abundance and alleviate jealousy.