Mahogany Obsidian
Volcanic Glass (Amorphous Silica) · Semi-Precious Gemstone / Decorative Stone
Crystal System
Amorphous (None); typically occurs in massive habits without internal crystalline structure due to rapid cooling.
Mineral Group
Silicates (specifically a mineraloid)
Chemical Formula
SiO2 (approx. 70-75%) with inclusions of Magnetite or Hematite (Fe2O3)
Formation Process
Igneous; formed when felsic lava volcanic material cools so rapidly that crystal growth is inhibited, resulting in a natural glass.
About This Crystal
An opaque to translucent volcanic glass characterized by a deep reddish-brown (mahogany) base with black swirls and mottling. It features a vitreous (glassy) luster and a smooth, highly reflective surface when polished.
Physical Characteristics
Color: Reddish-brown and black mottled; Streak: White; Cleavage: None; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35–2.60; Fluorescence: Generally none.
Optical Properties
Isotropic (singly refractive) due to its amorphous nature; Refractive Index: 1.48–1.51; No pleochroism or birefringence.
Hardness & Durability
Origin Region
Prominent in the United States (Oregon, California, Arizona), Mexico, and Japan; found in areas with recent geologically volcanic activity.
Hardness & Durability
Mohs Hardness: 5.0–5.5; Toughness: Brittle (easily chips or cracks); Stability: Sensitive to rapid temperature changes and physical impact.
Care & Maintenance
Clean with warm soapy water and a soft cloth; avoid ultrasonic or steam cleaners. Store separately from harder stones like quartz or sapphire to prevent scratching.
Rarity & Value
Common; relatively inexpensive and widely available. Value is determined by the balance of color patterns and the quality of the polish/cut.
Special Characteristics
The mahogany color is caused by varying concentrations of iron oxides (hematite or magnetite) trapped within the silica glass during solidification.
Lore & History
Historically used by ancient cultures for making sharp tools, mirrors, and arrowheads. In metaphysical traditions, it is associated with the Root and Sacral Chakras, believed to provide grounding, protection, and the release of inner limitations.