What it is

Mahogany obsidian is a variety of obsidian—a natural volcanic glass—distinguished by warm brown coloration juxtaposed with black. Because obsidian is amorphous (no long‑range crystal lattice), it’s classified as a mineraloid rather than a mineral.

Why “mahogany”?

The color echoes polished mahogany wood: deep red‑brown with subtle variations. In geological terms, that palette is made by iron oxides dispersed in the glass and by slight changes in oxidation during flow and cooling.

Flow banding

As silica‑rich lava moves, microscopic crystals (microlites), bubbles, and iron‑bearing melt segregate into ribbons. When the lava quenches to glass, those ribbons freeze as the mahogany and black bands you see.

Iron at work

Tiny iron‑oxide particles (hematite, magnetite, or their alteration products) and iron‑rich glass layers lend the brown tones. The size and concentration of these particles control how deep and “woody” the color appears.

Occasional extras

With time and gentle heat, parts of the glass can crystallize radial spherulites (the “snowflakes” seen in other obsidian). In mahogany material they’re less common but can appear as subtle gray blooms.

Palette

• Black — the base glass.
• Mahogany brown — from rust to brick‑red.
• Umber — darker, iron‑rich streaks.

Edges are typically translucent tea‑brown under strong light—classic obsidian behavior.

Pattern vocabulary

• Swirls & plumes: fluid brushstrokes of brown within black.
• Ribbons: parallel bands following the lava’s flow.
• Blotches: rounded “pools” of color where iron‑rich pockets paused.

Photo tip: Use side‑light at ~30° and a white bounce card opposite the light. The brown warms up, and the banding pops without glare.

Flow wisps

At 10×, look for fine, parallel wisps and streaks within both the black and brown. These are aligned microlites and tiny bubble trains captured by the flow.

Iron hints

Brown patches often show a soft, cloudy texture where sub‑microscopic iron phases scatter light. You won’t see discrete crystals—just a gentle haze compared to the glassy black.

Spherulites (occasional)

Rare, pale gray “snowflake” rosettes may occur—tiny radiating needles of cristobalite. They’re less common here than in classic snowflake obsidian.

Mahogany jasper / agate

Microcrystalline quartz (hardness ~7). Feels harder, takes a different polish, and lacks the glassy conchoidal shells seen on chipped obsidian.

Basalt (brown‑stained)

Fine‑grained rock with tiny crystals; matte to sub‑vitreous luster; edges are not “glassy.” Under magnification, crystals are visible instead of homogenous glass.

Industrial glass / slag

Can mimic color, but often shows frothy vesicles, metallic streaks, or swirled metallic sheen. Context (near old furnaces) is a clue.

Dyed composites

Uniform neon browns or repeating patterns suggest artificial composites. Natural mahogany obsidian shows organic, non‑repeating flow patterns.

Quick checklist

• Glassy luster + tea‑brown edges in strong light.
• Curved conchoidal fractures and sharp chips.
• Flow‑like brown swirls, not granular or banded agate textures.

At‑home tests

Shine a flashlight through a thin edge: mahogany zones glow warm brown; black reads smoky. A hand lens will reveal flow wisps rather than sugary grains.

Where it’s common

Found around felsic volcanic centers. Well‑known sources include parts of the western USA (e.g., Oregon’s obsidian fields), Mexico, and other rhyolitic provinces worldwide. It forms as rims and domes where lava chilled fast.

Geologic neighbors

Travels with other obsidians (black, sheen, rainbow), rhyolite, perlite (hydrated obsidian), and pumice from the same eruptions. Trace‑element “fingerprints” can tie pieces to their volcanic sources—an archaeological superpower.

Everyday handling

• Obsidian is brittle; avoid drops and hard impacts.
• Edges can be blade‑sharp. Handle rough chips like you would a knife.

Cleaning

• Lukewarm water + mild soap + soft cloth; rinse and dry.
• Avoid sudden temperature shocks—glass dislikes thermal whiplash.

Display & storage

• Store separately from harder quartz/corundum to keep a crisp polish.
• Side‑lighting around 30° pulls the brown forward beautifully.

Tea‑brown window

Hold a thin edge in front of a flashlight: the “black” turns warm brown, especially through the mahogany zones. It never gets old.

Conchoidal shell spotting

Under raking light, trace the curved ripples around a small chip. Each ripple is a frozen shock wave from the break.