Genuine Mexican material shows subtle sheen bands. Most 'rainbow obsidian' sold online is slag glass.
Iceland, Mexico, Oregon, Armenia, Turkey — anywhere rhyolitic lava cooled fast
There is a real material called rainbow obsidian, and it comes principally from Jalisco in Mexico. Its colour is not body colour: it is a sheen produced by aligned microscopic inclusions, and it appears as concentric or parallel bands of bronze, green, violet and gold that show only when the stone is cut and oriented correctly and viewed at the right angle. Turn the piece and the bands vanish, leaving plain black glass.
That behaviour is the whole test. If the colour is present from every angle and in every light, it is body colour, and obsidian does not have body colour in those hues. Bright, permanently coloured 'rainbow obsidian' beads are slag glass.
Cutting genuine material well is skilled work, because the sheen bands lie in a specific plane and a cabochon has to be oriented to them. That is why good examples cost more than the raw material suggests, and why cheap ones are usually not what they say.
These apply to this model and not to the rest of Obsidian. Work them alongside the maker's general checks, not instead of them.
Genuine rainbow obsidian's colour is an optical sheen from aligned inclusions and is visible only within a narrow range of angles. Rotate the stone and it should drop back to black. Colour that persists from every direction is body colour, which means glass.
Natural volcanic glass has no mechanism for vivid blue or purple body colour. Those hues in a solid, from-every-angle form indicate slag glass, which is full of metal oxides from smelting.
Even where the sheen bands are, the surrounding glass should show the stretched gas cavities and faint flow banding of a lava. A perfectly clean matrix with round bubbles is manufactured.
Genuine sheen material is modestly priced — low tens of dollars for a good cabochon oriented to show the bands.
An orientation for honest, unrestored condition — never an appraisal, and never a quotation.
Lovenhall StoneThe tests tell you what it is. The instrument reads a photograph and offers a name to start from — then hands you back to the tile and the coin, which are what settle it.