Glass. A milky blue-white glow, no play-of-colour, and no opal in it at all.
Australia (Lightning Ridge, Coober Pedy), Ethiopia, Mexico, Brazil
Opalite is manufactured glass, sometimes called sea opal or Tiffany stone in careless listings, and it contains no opal. Its effect is opalescence rather than play-of-colour: a soft milky blue-white glow from light scattering in the glass, which shifts warm against a light background and cool against a dark one.
The separation from opal is immediate once you know what to look for. Play-of-colour resolves into distinct patches of spectral colour — blue, green, gold, red — that flare and vanish as the stone moves. Opalite's glow never resolves into patches at all; it is uniform across the piece and simply brightens or dims.
Under a loupe, opalite also shows the usual signatures of glass: round trapped bubbles, occasional swirl lines, and a conchoidal fracture with no internal structure. It is hardness 5.5 or so and will not scratch a glass plate.
These apply to this model and not to the rest of Opal. Work them alongside the maker's general checks, not instead of them.
Opal's play-of-colour breaks into discrete patches of spectral colour that move and flare. Opalite produces a uniform milky glow with no patches at any angle. This is the whole difference and it is unmistakable side by side.
Opalite is glass, so a loupe usually finds spherical trapped bubbles and sometimes swirl lines. Natural opal contains no such spheres.
Cents to a few dollars. Manufactured glass sold under a mineral-sounding name.
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.