Flame Obsidian
Volcanic glass (silica-rich, ~70-75% SiO2, amorphous)
Black volcanic glass that flashes flame-like bands of iridescent color when light strikes aligned nanoscale inclusions.
- Mohs hardness
- 5-5.5
- Color
- Black with flame-like orange, gold, red, or rainbow sheen
- Type
- igneous
Got a rock like this?
Identify any rock from a photo, free.
Overview
Flame Obsidian is a trade name for obsidian that, when angled to the light, reveals flame-shaped streaks of fiery iridescence, oranges, reds, golds, and rainbow hues, against a black body. It is closely related to fire obsidian and rainbow obsidian, all of which owe their color to optical interference rather than pigment.
The stone itself is ordinary black volcanic glass. The flame effect comes from thin layers of aligned nanometer-scale inclusions (commonly magnetite) that act like a diffraction or thin-film interference structure.
It is highly prized among obsidian collectors for the intensity and movement of its color flashes.
Formation & geology
The host glass forms by rapid cooling of silica-rich lava. During flow, extremely fine magnetite (iron oxide) nanoparticles became concentrated into thin, parallel layers within the melt.
When light passes through and reflects off these closely spaced layers, thin-film interference produces vivid iridescent colors, the same physics behind soap-bubble color. Because the layers follow the lava's flow contours, the iridescence appears in flame-like sweeps. The effect is only visible at certain viewing angles and is concentrated in specific bands, so cutting orientation is critical for lapidaries.
How to identify it
Base identification is obsidian: glassy luster, conchoidal fracture, sharp edges, hardness ~5-5.5, white streak. The defining feature of Flame Obsidian is angle-dependent flame-shaped iridescence, color that shifts and disappears as you tilt the stone.
The iridescence is internal and directional, not a surface coating or dye.
Look-alikes: rainbow obsidian (broader, more sheet-like color bands), fire obsidian (concentric fiery layers), and labradorite (a feldspar with labradorescence but higher hardness ~6-6.5 and crystalline, not glassy). True flame obsidian's sharp conchoidal fracture confirms the glass.
Uses & significance
Flame Obsidian is a sought-after lapidary material for cabochons and collector specimens, where the cut is oriented to maximize the flame display. Quality iridescent pieces command higher prices than ordinary obsidian.
It is used in statement jewelry and display pieces rather than industrial applications.
Metaphysically it is linked to passion, energy, and transformation, claims that are spiritual in nature, not scientific.
Frequently asked questions
What causes the flame colors in Flame Obsidian?
Thin parallel layers of nanoscale magnetite inclusions create thin-film interference, producing iridescent flame-like color flashes that change with viewing angle.
Is Flame Obsidian dyed or coated?
No. The color is a natural optical interference effect from internal inclusions; it is not pigment, dye, or surface coating.
How is it different from rainbow obsidian?
Both share the same cause, but flame obsidian shows fiery, flame-shaped bands while rainbow obsidian typically displays broader sheets or rings of color.
Why does the color disappear when I tilt it?
Iridescence is angle-dependent; the interference colors are only visible when light hits the aligned inclusion layers at the right angle.
Flame Obsidian guides
In-depth guides for identifying, valuing, and understanding Flame Obsidian.
