Obsidian
Volcanic Glass (Amorphous Silica) · Decorative Stone / Mineraloid / Semi-Precious Gemstone
Crystal System
Amorphous (Non-crystalline); Typically occurs in massive, blocky, or flow-banded habits.
Mineral Group
Silicates (Mineraloid)
Chemical Formula
SiO2 (70–75%) + MgO, Fe3O4 (Inclusions)
Formation Process
Igneous: Forms when felsic lava cools extremely rapidly (quenching), preventing crystalline growth.
About This Crystal
A dense, volcanic glass with a smooth, uniform texture. This specimen shows a matte grey to black weathered exterior with sharp, angular edges and large conchoidal fracture faces. It is opaque to translucent on thin edges with a vitreous to dull luster.
Physical Characteristics
Color: Gunmetal grey to jet black; Streak: White; Cleavage: None; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35–2.6; Tenacity: Very brittle.
Optical Properties
Refractive Index: 1.450–1.550 (Singly Refractive); No pleochroism or birefringence due to amorphous structure.
Hardness & Durability
Origin Region
Volcanic regions such as Oregon and California (USA), Iceland, Mexico, and the Lipari Islands (Italy).
Hardness & Durability
Mohs Hardness: 5–5.5; Low toughness (easily chips); High chemical stability; Brittle nature restricts wearability in rings.
Care & Maintenance
Clean with warm soapy water and soft brush; avoid ultrasonic cleaners and mechanical impacts; store separately to prevent scratching.
Rarity & Value
Common; Value is determined by color variants (Rainbow/Sheen) and size. Generally inexpensive as a raw mineral.
Special Characteristics
Exhibits distinct conchoidal fracturing creating razor-sharp edges; occasionally displays snowflake patterns (cristobalite) or metallic sheen.
Lore & History
Historically used by Neolithic cultures for surgical tools, arrowheads, and mirrors. Metaphysically associated with protection and grounding (Root Chakra).