The name spinel may come from the Latin spina or “thorn,” referring to the triangular shape of the crystal faces, or from the Greek root spinter, meaning "spark," presumably referring just to the red variety. Like ruby and garnet, it has also been called “carbuncle," from the Latin carbunculus, or “small coal." However, recognition that the various types of carbuncle differed in hardness, led to their being valued accordingly. Undesirable confusion has been created by the alternative name of ruby spinel; and In fact, some of the largest and most famous “rubies" in the world, such as the "Black Prince's Ruby" in the English crown jewels, are really spinels, not corundums.
Appearance Spinel may be an intense, bright redllke ruby", but more often tends to be brick red, almost orange
lt can have a violet tinge, and such stones were formerly referred to as Balas ruby, after the Badakshan (Balascia) region of Afghanistan where they were found. The color often soft: pink, rather than red. Spinel has good luster and transparency. It is generally given a mixed, oval or round cut; alternatively, a square or rectangular, step or trap cut. in earlier times, perfectly-octahedral crystals were used In jewelry as they were, uncut, like diamonds. Stones found as worn pebbles or. _irre_gu|ar pieces were summarily rounded and then polished, like some large spinels now seen in museums.
Distinctive features Red spinel is fairly similar to ruby; the red color fluoresces slightly in bright light, but much less than ruby. Being singly refractive, it is not pleochrolc. This feature is in contrast to ruby but in common with garnet, although the latter is nearly always a rather dull color, which is not heightened even by strong light. It can be hard to distinguish spinel from either of these gemstones, In which case the physical properties will need to be measured. However, spinel may contain several parallel rows of minute octahedral crystals of ‘hercynite (iron spinel), which are highly distinctive and sometimes recognizable with an ordinary lens. Soft pink varieties can be hard to distinguish from some tourmalines, although the latter display varying degrees of birefringence, and have different physical properties.
Occurrence Red and pink spinels come from the Mogok region of Burma and Afghanistan. Spinels may also come from Sri Lanka and Thailand, where they are found together with corundum.
Value As secondary gems go, brilliant red spinels comparable in color to rubies are quite valuable, though they are only one-tenth or so the price of rubies themselves.
Pale pink or violet spinels, except for particularly fine or large specimens, are of much lower value.
Simulants and synthetics Synthetic spinel in many colors has been widely produced by the flame fusion method, but owing to difficulties in obtaining the red variety, the only examples found are extremely raFe and of small size—a maximum of one carat or little more. These are distinguished from the natural variety by the typical internal structure and inclusions of gems produced by the Verneuil method. Recently, synthetic red spinel has also been produced by the more costly flux melt process, but it has not proved economical.