Black Obsidian
Volcanic Glass var. Obsidian · Decorative Stone / Semi-Precious Gemstone
Crystal System
Amorphous (Non-crystalline)
Mineral Group
Mineraloid
Chemical Formula
SiO2 with impurities (MgO, Fe3O4)
Formation Process
Igneous process formed by the rapid cooling of felsic lava without crystal growth
About This Crystal
A smooth, tumbled, jet-black stone exhibiting a vitreous to glossy luster and opaque transparency, characteristic of a high-silica volcanic glass.
Physical Characteristics
Black body color, white streak, conchoidal fracture with extremely sharp edges, specific gravity around 2.35 - 2.45, brittle tenacity.
Optical Properties
Singly refractive (isotropic due to amorphous structure), refractive index of approximately 1.48 - 1.51.
Hardness & Durability
Origin Region
United States, Mexico, Iceland, Italy, Japan
Hardness & Durability
Mohs hardness of 5 to 5.5, moderate to low toughness due to easy conchoidal fracturing.
Care & Maintenance
Clean with warm soapy water and a soft cloth; avoid ultrasonic cleaners and harsh chemicals; store separately to prevent scratching.
Rarity & Value
Common, highly affordable, widespread globally, with values depending on size, polish, and special optical phenomena like sheen or rainbow effects.
Special Characteristics
Smooth tumbled finish showcasing high glossy reflectivity; lacks true crystalline structure.
Lore & History
Historically used by ancient Mesoamerican cultures for arrowheads, blades, and mirrors; traditionally associated with grounding, protection, and clearing negative energy in modern crystal healing lore.