Mahogany Obsidian
Volcanic Glass (Amorphous Silica) · Semi-Precious Gemstone / Igneous Rock
Crystal System
Amorphous (No crystal system); typically occurs in massive or globular habits because it cools too quickly for crystals to grow
Mineral Group
Silicates (Non-crystalline Volcanic Glass)
Chemical Formula
SiO2 (70–75%) with inclusions of Fe2O3 (Hematite or Magnetite)
Formation Process
Igneous: Forms when high-silica lava cools extremely rapidly upon contact with air or water, preventing atomic crystallization; the 'mahogany' streaks are caused by localized concentrations of iron oxides
About This Crystal
An opaque to translucent volcanic glass characterized by a deep reddish-brown and black mottled appearance. It exhibits a vitreous (glassy) luster and a smooth, even texture particularly when tumbled. The patterns are usually swirling or splotchy.
Physical Characteristics
Color: Black with reddish-brown streaks/spots; Streak: White; Cleavage: None; Fracture: Conchoidal (shell-like); Specific Gravity: 2.35–2.60; Tenacity: Brittle; Fluorescence: Generally none.
Optical Properties
Isotropic (Singly refractive); Refractive Index: 1.48–1.51; Luster: Vitreous; Transparency: Opaque to translucent on thin edges.
Hardness & Durability
Origin Region
Western USA (notably Oregon, California, Utah), Mexico, and Afghanistan; typically found in rhyolitic volcanic regions
Hardness & Durability
Mohs Hardness: 5.0–5.5; Toughness: Poor (fragile and prone to chipping); Stability: Stable to light but sensitive to sudden temperature changes and physical impact.
Care & Maintenance
Clean with warm soapy water and a soft cloth; avoid ultrasonic cleaners and steam cleaning. Store separately from harder stones like quartz or sapphire to prevent scratching.
Rarity & Value
Common; Very affordable; Value is determined by the balance and beauty of the mahogany-to-black patterning; prices typically range from $1–$10 for tumbled stones.
Special Characteristics
Distinctive conchoidal fracture which creates razor-sharp edges; unique 'flow' patterns of iron-rich impurities within the silica matrix.
Lore & History
Historically used for making extremely sharp cutting tools, arrowheads, and mirrors. In metaphysical traditions, it is associated with the Root Chakra and is believed to offer protection and grounding, helping to remove energy blockages and provide strength.