Aurora Obsidian
Volcanic glass (~70-75% SiO2)
A trade name for rainbow-sheen obsidian whose aligned nanoparticles produce shifting aurora-like bands of color.
- Mohs hardness
- 5-5.5
- Color
- Black with multicolor iridescent sheen
- Type
- igneous
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Overview
Aurora Obsidian is a trade name for a high-grade rainbow obsidian, natural volcanic glass that displays broad, shifting bands of iridescent color, said to recall the aurora (northern lights). The body is black, but tilting the polished stone reveals greens, golds, purples, blues, and pinks.
The color is not pigment but an optical effect: layers of aligned nanoscale inclusions (often magnetite microcrystals) act like thin films, scattering light into spectral colors.
As obsidian it is amorphous glass with conchoidal fracture and a brilliant polish. 'Aurora' is a marketing label, so the term overlaps heavily with premium rainbow and sheen obsidian.
Formation & geology
Aurora Obsidian forms like all rainbow obsidian: silica-rich lava cools so fast it freezes into glass, trapping flow-aligned layers of extremely fine inclusions, commonly nanoscale magnetite crystallites and oriented bubbles.
These ordered layers behave as natural thin films and diffraction structures. When light passes through and reflects off successive layers, interference selectively reinforces certain wavelengths, producing the sweeping iridescent colors.
The richest, most multicolored material, marketed as aurora, comes mainly from Mexican obsidian flows, the same source as much commercial rainbow obsidian.
How to identify it
Identify it as a black, glassy stone that flashes broad, multicolored iridescent bands when tilted under a single bright light; the colors shift and move rather than staying fixed. Hardness is 5-5.5, luster vitreous, fracture conchoidal, streak white.
The iridescence is strongest on polished, correctly oriented surfaces. Without the right angle the stone simply looks black.
Distinguish it from labradorite (crystalline feldspar, harder, with cleavage and a different blue-green schiller) and from fire obsidian (which shows thin-film color in a more layered, patchy way). Aurora obsidian's smooth glass fracture and softness confirm it is obsidian.
Uses & significance
Aurora Obsidian is cut into cabochons, spheres, hearts, and beads angled to maximize the rainbow flash; it is popular in pendants and display pieces. It polishes to a mirror finish but, as glass, can chip and is best set protectively.
Obsidian generally has a long history as a tool, weapon, and mirror material.
Metaphysically, rainbow and aurora obsidian are associated with joy, hope, and protection, with the spectral colors said to lift mood; these are traditional beliefs, not scientific facts.
Frequently asked questions
Is aurora obsidian the same as rainbow obsidian?
Essentially yes. 'Aurora obsidian' is a trade name for premium, vividly multicolored rainbow obsidian. Both get their color from aligned nanoscale inclusions.
What causes the rainbow colors?
Thin layers of aligned nanoparticles (often magnetite) act like natural thin films, scattering light into shifting spectral bands, an optical effect, not dye.
Why does my piece look plain black sometimes?
The iridescence only appears at the correct angle under directed light. From other angles the stone looks solid black.
Is aurora obsidian natural?
Yes, the material is natural rainbow obsidian. The 'aurora' name is a marketing term, not an indication of treatment.
Aurora Obsidian guides
In-depth guides for identifying, valuing, and understanding Aurora Obsidian.
