Identifying Synthetic Moissanite

(via Gems & Jewellery News, December 1998) Jamie Nelson writes:

If a large batch of unmounted diamonds of a range of sizes requires to be checked to determine if the batch has been salted with synthetic moissanites, then there is an easy alternative method to the methylene iodide sink or float separations.

Place the stones, table down, on the bottom of a shallow, flat bottomed, clear glass dish and cover all the stones completely with tap water. The much higher optical dispersion of moissanite (0.104 or almost x 2½ that of diamond) will reveal itself as bright spectral colored flashes, while diamonds (dispersion 0.044) will display less brightly colored sparkles. The method will still work with open-backed bracelets, necklaces and other items provided that all the stones lie table down (i.e. culet uppermost).

This being so, in the case of a finger ring mounted moissanite, the only piece of equipment needed to ensure a confident distinction is a battery-operated hand-held polariscope. The ring is placed between the polars so that the place of the stone’s table lies parallel to the optic axis of the polariscope, i.e. the long torch battery stem. The polariscope is then rotated in the axis of the torch barrel while keeping the ring stationary.

If the stone is moissanite, the usual winking of the stone’s image will be seen. If it is diamond, little or no change in the scattered light intensity will be observed. If the colorless stone happens to be another uniaxial or biaxial material, such as zircon, rutile, lithium niobate, corundum, scheelite, zincite, topaz or enstatite, then of course winking effects also will be seen. But all will be unable to pass a scratch-hardness test using the sharp edge of a carborundum (alpha silicon carbide) monocrystal applied cautiously to the girdle. However, our concern here is only to disclose the presence of moissanite and not to identify a nondiamond stone.