Mahogany Obsidian Identification Guide
A guide to identifying Mahogany Obsidian, a brown-and-black volcanic glass, by its color banding, glassy fracture, and look-alikes.
Read the full Mahogany Obsidian encyclopedia entry →
What Mahogany Obsidian Looks Like
Mahogany Obsidian is a natural volcanic glass colored in rich reddish-brown ("mahogany") and black, with the brown caused by iron oxide inclusions in the glass. Like all obsidian it is amorphous (non-crystalline).
- Color: reddish-brown to mahogany, mottled or banded with black
- Luster: vitreous (bright glassy shine)
- Transparency: translucent on thin edges to opaque
- Habit: amorphous glass; massive with conchoidal fracture and very sharp edges
Step-by-Step Field ID Checklist
- Look for the brown-and-black swirling/banded color — the defining mahogany pattern.
- Check the luster — bright glassy shine on broken surfaces.
- Confirm conchoidal fracture — smooth, curved, shell-like breaks with razor edges.
- Hold a thin edge to light — obsidian is translucent at the edges.
- Test hardness — about 5-5.5; quartz scratches it.
Key Diagnostic Tests
- Mohs hardness: 5-5.5.
- Streak: white.
- Cleavage: none; conchoidal fracture.
- Specific gravity: ~2.35-2.5, light.
- Optics: isotropic (it is glass), no crystals under magnification (may show flow bands/inclusions).
Common Look-Alikes and How to Tell Them Apart
- Other obsidians (black, snowflake, rainbow): same glass; distinguished by color/inclusions. Mahogany is defined by its brown-and-black coloring.
- Jasper (brown/red): jasper is microcrystalline, harder (7), fully opaque, and lacks obsidian's glassy translucent edges.
- Smoky/brown glass slag (man-made): look for abundant uniform bubbles and unnaturally even color.
- Tektite: also natural glass but typically pitted/etched black-brown; mahogany obsidian shows volcanic banding rather than sculpted surfaces.
Where It Is Typically Found
Mahogany Obsidian forms in rhyolitic lava flows. It is common in the western USA — Oregon, California, Nevada, Utah, and Arizona — and other young volcanic regions worldwide.
Frequently asked questions
What is Mahogany Obsidian?
Mahogany Obsidian is a natural volcanic glass colored reddish-brown and black, with the mahogany tones produced by iron oxide inclusions. It is amorphous, glassy, and breaks with sharp conchoidal fractures.
How can you tell if Mahogany Obsidian is real?
Real obsidian is a glass: vitreous luster, conchoidal fracture, translucent on thin edges, Mohs 5-5.5, and light (SG ~2.4). Man-made glass usually shows abundant uniform bubbles and overly even color.
Mahogany Obsidian vs jasper?
Jasper is microcrystalline quartz — harder (Mohs 7), fully opaque, and not glassy — while mahogany obsidian is volcanic glass with a glassy shine and translucent edges. A hardness test separates them.
What gives Mahogany Obsidian its brown color?
The reddish-brown mahogany color comes from iron oxide (hematite/limonite) inclusions distributed through the otherwise black volcanic glass, often forming bands or mottling.
Mahogany Obsidian identified by the community
Recent Mahogany Obsidian specimens identified with Rock Identifier.
