Black Obsidian
Volcanic Glass var. Obsidian · Decorative Stone and Mineral Specimen
Crystal System
Amorphous (Non-crystalline)
Mineral Group
Mineraloid
Chemical Formula
SiO2 (Silicon Dioxide with variable trace impurities such as Fe and Mg)
Formation Process
Extrusive igneous process formed by the rapid cooling of felsic lava without sufficient time for crystal growth
About This Crystal
A dark, deep black, glossy, and opaque specimen with a characteristic glassy luster and sharp, conchoidal fracture surfaces reflecting light.
Physical Characteristics
Color is deep black to dark brown; streak is white; no cleavage; fracture is distinctly conchoidal; specific gravity is approximately 2.35 to 2.50; tenacity is brittle.
Optical Properties
Isotropic with a refractive index of approximately 1.48 to 1.51; displays a vitreous to resinous luster.
Hardness & Durability
Origin Region
Global volcanic regions including the United States, Mexico, Iceland, Italy, and Japan
Hardness & Durability
Mohs hardness is 5 to 5.5; relatively brittle with sharp edges that require careful handling; moderate durability for jewelry if protected.
Care & Maintenance
Clean with mild soap and warm water; avoid harsh chemicals, ultrasonic cleaners, and sudden extreme temperature changes; store separately to avoid scratching softer stones.
Rarity & Value
Common and widely available; value is generally low to moderate depending on size, carving quality, or optical varieties such as sheen obsidian.
Special Characteristics
Breaks with extremely sharp conchoidal edges historically used for cutting tools and arrowheads; can exhibit sheens or snowflake patterns due to micro-crystallization.
Lore & History
Historically used by ancient civilizations for tools, mirrors, and weapons; in modern metaphysical practices, it is associated with the root chakra and believed to offer psychic protection and grounding energy.