Spinel, as rough, this unusual gemstone sometimes appears as intensely red crystals in perfect octahedral shape - the famed Burmese "anyan nat thwe" or "cut by the spirits".
Spinel is a single refractive stone with an index as high as 1.72-1.80. This property makes spinel a friendly and forgiving stone to cut. Even flat spinel stones will have a nice distinctive fire. Its hardness of 8 on the Moh's scale is an advantage for both cutter and stone setter. Spinel's specific gravity of 3.58-3.61 makes it 10% lighter than Ruby; which means more stones per carat weight for melees. Gemcal's spinel is a natural and treatment-free stone; no glass filling or heat treatments. With these facts in mind, plus the formidable problem of obtaining rubies with equal color and clarity in the same price range, it becomes easy to understand why spinel is becoming such a sought after gem.