Obsidian with Feldspar Inclusions
Volcanic Glass with Plagioclase Feldspar phenocrysts · Mineraloid / Semi-Precious Gemstone
Crystal System
Amorphous (Glassy) matrix with Triclinic crystalline inclusions
Mineral Group
Silicates (Tectosilicate class)
Chemical Formula
SiO2 (approx. 70–75%) with Al, Na, K, Ca impurities
Formation Process
Igneous: Rapid cooling of silica-rich (felsic) lava preventing crystallization, with slower-forming inclusions
About This Crystal
A dark, glassy volcanic rock featuring a vesicular, porous surface texture. It is predominantly opaque black with an earthy to vitreous luster, containing white to greyish phenocryst inclusions of feldspar.
Physical Characteristics
Black body color; white streak; conchoidal fracture in glass parts, uneven in vesicular parts; specific gravity 2.4; non-magnetic; no fluorescence.
Optical Properties
Isotropic (glass) with anisotropic inclusions; refractive index 1.48-1.51; generally opaque to translucent on thin edges.
Hardness & Durability
Origin Region
Volcanic regions such as Mexico, Iceland, Western USA (Oregon/Utah), and Armenia
Hardness & Durability
Mohs hardness 5.0 - 5.5; brittle toughness; sensitive to sudden temperature changes and physical impact.
Care & Maintenance
Clean with warm soapy water only; avoid ultrasonic cleaners and steam; store separately to prevent scratching from harder stones.
Rarity & Value
Common; low to moderate value; price determined by unique patterns and size; treatments are rare for this variety.
Special Characteristics
Vesicular structure (gas bubbles) and porphyritic texture (distinct large crystals embedded in a fine-grained or glassy matrix).
Lore & History
Historically used for tool-making and mirrors; traditionally associated with grounding, protection, and the root chakra in folklore.