Sold as moonstone, but mineralogically white labradorite. The blue is labradorescence, not adularescence.
Madagascar, Finland (spectrolite), Labrador in Canada, Russia
Rainbow moonstone is a trade name, and mineralogically it is not moonstone at all: it is white or colourless labradorite. True moonstone is orthoclase feldspar, and its glow is adularescence — a soft billowy sheen that seems to float inside the stone and moves with it. Rainbow moonstone's colour is labradorescence, the same lamellar interference effect as grey labradorite, appearing as distinct flashes of blue at specific angles.
The two are easy to tell apart once described. Adularescence is a diffuse cloud of light, usually blue-white, that appears to hover beneath the surface and drifts as the stone tilts. Labradorescence is a flat sheet of saturated colour that snaps on and off. Rainbow moonstone typically also shows visible internal fractures and a stronger, more electric blue than genuine moonstone's soft glow.
Neither is a fraud — the name is simply loose, and it is well established in the trade. It matters because fine orthoclase moonstone with a clean, strong, floating blue sheen is a scarcer and more valuable material than white labradorite.
These apply to this model and not to the rest of Labradorite. Work them alongside the maker's general checks, not instead of them.
Adularescence — true moonstone — is a soft, diffuse, billowing cloud of light that drifts beneath the surface as the stone moves. Labradorescence is a flat sheet of saturated colour that appears and disappears abruptly at particular angles. Rainbow moonstone does the latter.
Rainbow moonstone commonly shows visible internal cracks and feathers, which many buyers accept as part of the material. Fine orthoclase moonstone is valued for clarity, so heavy internal fracturing points towards labradorite.
Inexpensive to modest. Clean pieces with strong blue flash run tens of dollars.
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.