Synthetic Spinel

Gemmology Queensland writes:

Synthetic spinels were first grown by the flame fusion method of synthesis. These early synthetics, which owed their colors to a range of transitional metal chromophores, are easily identified by their high specific gravity of 3.63 and higher refractive index of 1.728. Flux grown synthetic spinels, that primarily originate from Russia are either red or blue in color. As the Russian flux-grown spinels are grown with a 1:1 Al:Mg ratio, their single refractive index (1.71/1.72) and specific gravity (3.60/3.62) are near identical to those of natural spinel color. Fortunately, the presence of solid metalic flux inclusions, and/or reflective grayish platinum will identify flux-grown spinels of Russian origin.

Another synthetic spinel of gemological interest includes a dark blue sintered mass of synthetic spinel powder together with cobalt oxide and specks of gold that has been marketed as a lapis imitation since the early 1950s. This imitation is identifiable by its non-pyrite brassy specks, its brilliant red color when viewed through a Chelsea filter, and its unusually low specific gravity of 3.52.

Synthetic spinel also have been used in the manufacture of an imitation moonstone. This imitation displays a distinct schiller that is thought to be induced into the synthetic spinel by heat treatment. However the distinctive blue-white fluorescence of this imitation when examined under shortwave ultraviolet light readily identifies it.