Mahogany obsidian is a natural volcanic glass characterized by its distinct reddish-brown and black swirling patterns caused by iron oxide inclusions. It forms when lava cools so rapidly that crystalline structure is prevented, resulting in a smooth, glass-like texture that fractures conchoidally.
Is this mahogany obsidian?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch mahogany obsidian with a known reference. Mahogany Obsidian sits at Mohs 5-6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Mahogany Obsidian leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Mahogany Obsidian typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: red-brown, black.
- 5Look at form & habitTypical habit: massive.
Often confused with
Mahogany Obsidian vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Luster reads vitreous on Mahogany Obsidian and waxy on Agate.
How to tell apart: Luster reads vitreous on Mahogany Obsidian and waxy on Jasper.
How to tell apart: Flint Nodules is the harder of the two (Mohs 7 vs. 5-6); luster reads vitreous on Mahogany Obsidian and waxy on Flint Nodules.
Often found alongside mahogany obsidian
Minerals reported to co-occur with mahogany obsidian. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂
- Mohs hardness
- 5-6
- Density
- 2.4 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Opaque
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Volcanic Rhyolite
- Typical price
- $5-30 for rough slabs and polished stones
Where rockhounds find mahogany obsidian
Classic worldwide localities
- Oregon, USA
- California, USA
- Mexico
Field-hunting tip
Look in volcanic rhyolite country — that is the host setting where mahogany obsidian typically forms. If you start seeing quartz, feldspar, cristobalite in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find mahogany obsidian on the map
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