Black Obsidian
Obsidian (Volcanic Glass) · Semi-Precious Gemstone / Igneous Rock
Crystal System
Amorphous (Non-crystalline); lacks a systematic internal structure
Mineral Group
Silicates (Mineraloid)
Chemical Formula
SiO2 (70-75%) + MgO, Fe3O4
Formation Process
Igneous: Forms when high-silica felsic lava cools extremely rapidly (quenched) at the Earth's surface, preventing the growth of mineral crystals.
About This Crystal
A jet-black, opaque to slightly translucent volcanic glass with a smooth, vitreous (glassy) luster. This specific specimen is carved into a polished heart shape roughly 1.5-2 cm in width. It features a highly reflective surface and deep uniform coloration.
Physical Characteristics
Color: Black; Streak: White; Cleavage: None; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35–2.60; Fluorescence: Generally inert; Tenacity: Brittle with very sharp edges when fractured.
Optical Properties
Refractive Index: 1.450–1.550; Isotropic (Singly Refractive); Luster: Vitreous; Optical phenomena: Can show golden or silver sheen (sheen obsidian) or rainbows (rainbow obsidian) depending on inclusions.
Hardness & Durability
Origin Region
Mexico (notably Jalisco and Hidalgo), USA (Oregon, California), Iceland, and Italy (Lipari islands). Forms in areas of recent volcanic activity.
Hardness & Durability
Mohs Hardness: 5.0–5.5; Toughness: Low (brittle and prone to chipping); Stability: Stable against light, but sensitive to high heat and sharp impacts.
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 scratching.
Rarity & Value
Common; relatively inexpensive. Value increases for varieties with optical effects like 'Sheen' or 'Rainbow'. Highly valued for lapidary work and sharp-edged tools.
Special Characteristics
Known for its conchoidal fracture which produces edges thinner and sharper than high-quality steel scalpels. May contain microscopic mineral inclusions of magnetite or hematite.
Lore & History
Historically used by Mayans and Aztecs for mirrors and sacrificial blades. Pliny the Elder named it after Obsidius, a Roman explorer. In metaphysical lore, it is considered a 'stone of protection' and 'truth-seeker' associated with the Root Chakra.