Peridot in Basalt
Forsterite (Olivine) in Vesicular Basalt · Mineral Specimen / Semi-Precious Gemstone (when gem-quality crystal centers are present)
Crystal System
Orthorhombic system; typically found as rounded granular grains or orthorhombic prisms when well-formed.
Mineral Group
Silicates (Nesosilicates); Olivine Group
Chemical Formula
(Mg,Fe)2SiO4 (Olivine series)
Formation Process
Igneous: Forms deep within the Earth's mantle and is carried to the surface by basaltic magma. These crystals often represent xenoliths (foreign rocks) or phenocrysts trapped in cooling lava.
About This Crystal
Greenish-yellow granular crystals embedded in a dark, fine-grained volcanic matrix. The crystals vary from translucent to transparent with a vitreous (glassy) luster, while the host rock is opaque and dull.
Physical Characteristics
Color: Olive green to yellow-green. Streak: White. Cleavage: Poor/Indistinct. Fracture: Conchoidal to uneven. Specific Gravity: 3.27–3.37. Moderate fluorescence is rare but can occur under UV.
Optical Properties
Refractive Index: 1.635–1.690. Birefringence: 0.035–0.038. Pleochroism: Weak (yellow-green to green). Doubly refractive.
Hardness & Durability
Origin Region
Notable sources include Peridot Mesa, San Carlos Apache Reservation, Arizona, USA; Canary Islands; and various volcanic fields in Hawaii.
Hardness & Durability
Mohs Hardness: 6.5–7. Brittle toughness; sensitive to thermal shock and rapid temperature changes.
Care & Maintenance
Clean with warm soapy water only. Avoid ultrasonic cleaners and steam cleaning. Protect from acids and sharp blows due to brittleness.
Rarity & Value
Common as small grains in basalt; gem-quality crystals over 1 carat are uncommon. Value is determined by the size and clarity of the green inclusions.
Special Characteristics
As a rock-xenolith, the specimen often displays a 'sugary' granular texture known as dunite when the olivine concentration is high.
Lore & History
Ancient Egyptians called Peridot the 'gem of the sun.' Historically used as a protective stone in amulets. In modern lore, it is believed to assist in emotional balance and manifestation.