Rainbow Obsidian
Obsidian (Amorphous Volcanic Glass) · Semi-Precious Gemstone / Volcanic Glass
Crystal System
Amorphous (Non-crystalline); habit is typically massive or as rounded volcanic inclusions (Apache Tears)
Mineral Group
Silicates (specifically a Mineraloid)
Chemical Formula
SiO2 (approx. 70–75%) with MgO, Fe3O4, and various mineral inclusions
Formation Process
Igneous: Forms when high-silica intermediate or felsic lava cools extremely rapidly, preventing the growth of crystal structures
About This Crystal
An opaque, black volcanic glass that displays concentric iridescent bands of color when polished and exposed to bright light. It has a vitreous (glassy) luster and a smooth, curved surface with conchoidal texture.
Physical Characteristics
Color: Black to dark brown with multicolored internal bands; Streak: White; Cleavage: None; Fracture: Conchoidal (shell-like); Specific Gravity: 2.35–2.60; Fluorescence: Generally inert
Optical Properties
Refractive Index: 1.48–1.51 (Singly Refractive); Optical Phenomena: Iridescence caused by oriented nanoscopic inclusions of magnetism or pyroxene and microscopic bubbles
Hardness & Durability
Origin Region
La Cholila, Mexico; Jalisco, Mexico; and various volcanic regions in the USA (Oregon, California)
Hardness & Durability
Mohs Hardness: 5.0–5.5; Toughness: Brittle; Stability: Sensitive to sudden temperature changes and physical impact; susceptible to scratching
Care & Maintenance
Clean with warm soapy water and a soft cloth; avoid ultrasonic or steam cleaners. Store separately from harder stones like quartz or topaz to prevent scratches.
Rarity & Value
Relatively common; value is determined by the brightness and variety of colors in the 'rainbow' bands. Prices are generally affordable for collectors.
Special Characteristics
Displays distinct 'sheen' or 'rainbow' effect when oriented correctly under light, often revealing green, purple, gold, or blue circular or linear bands.
Lore & History
Historically used for making sharp tools, arrowheads, and mirrors. Metaphysically, it is traditionally associated with the Root Chakra and believed to provide psychic protection and help in 'cutting' emotional ties.