Peridot in Basalt
Olivine (var. Peridot) in Porphyritic Basalt · Mineral Specimen / Semi-Precious Gemstone
Crystal System
Orthorhombic; Habit is typically granular, glassy masses or rounded grains (xenocrysts) within the volcanic matrix.
Mineral Group
Silicates (Nesosilicates); Olivine Group
Chemical Formula
(Mg, Fe)2SiO4 (Magnesium Iron Silicate)
Formation Process
Igneous; forms deep in the Earth's mantle and is carried to the surface by basaltic magma during volcanic eruptions. Crystallizes at high temperatures (~1200-1900°C).
About This Crystal
Translucent to transparent olive-green grains embedded in a dark gray to black, fine-grained (aphanitic) or vesicular volcanic basalt matrix. The crystals exhibit a vitreous luster and lack visible cleavage planes.
Physical Characteristics
Color: Olive-green to lime-yellow; Streak: White; Fracture: Conchoidal; Specific Gravity: 3.27–3.37; Tenacity: Brittle; Fluorescence: None.
Optical Properties
Refractive Index: 1.635–1.690; Birefringence: 0.033–0.038 (high); Pleochroism: Weak (yellow-green to green); Doubly refractive.
Hardness & Durability
Origin Region
Notable sources include San Carlos Apache Reservation (Arizona, USA), Lanzarote (Canary Islands), and Peridot Mesa. Often found in mafic and ultramafic volcanic rocks.
Hardness & Durability
Mohs Hardness: 6.5–7.0; Toughness: Fair to Good; Sensitivity: Sensitive to rapid temperature changes and sulfuric acid.
Care & Maintenance
Avoid ultrasonic and steam cleaners. Clean with warm soapy water and a soft brush. Mineral specimens should be kept away from harsh chemicals and protected from physical impact as the basalt can be crumbly.
Rarity & Value
Common as a mineral specimen; value is based on the size and clarity of the green inclusions. Higher value for larger, facet-grade crystals separated from the matrix.
Special Characteristics
Often presents as 'xenocrysts' (foreign crystals) within the basalt, representing fragments of the Earth's upper mantle (peridotite).
Lore & History
Historically known as 'the gem of the sun' by ancient Egyptians. It has been mined for over 3,500 years. Traditionally associated with the heart chakra, it is believed to inspire happiness and ward off nightmares.