Because it is so rare, spinel has hardly had a chance to become popular, and that lack of demand has kept the price low--for now. Spinel is one of few gemstones that require no special treatments; its beautiful, vivid colors and clarity are entirely natural.
It isn't difficult for a gemologist to differentiate between spinel and ruby or sapphire. Spinel may look like corundum, but it has different chemical, optical and physical properties. Spinel is not as hard or as dense as corundum, but at 8 on the hardness scale, it is still one of the more durable gems. It also has many other discrete characteristics. The most notable difference between the two is crystal structure. Spinel belongs to the cubic system and, unlike corundum, is singly refractive. The fastest and easiest way to separate the two gems is by looking for double refraction or its absence. Because this is not always so easy to detect on all stones, dichroism, spectrum and refractive index are other good separations.
Chemically, spinel is a magnesium aluminum oxide, its chemical formula represented as MgAl2O4. Nature rarely creates anything quite that pure. Many other elements are often present in varying amounts, creating a wider range of values for many of spinel's properties. Iron, manganese, chromium and zinc are the most common replacements for magnesium.
Spinel is found in some of the most exotic and nearly inaccessible parts of Earth. Myanmar (Burma) and Sri Lanka are two of the best-known spinel sources, but spinel is also found in Afghanistan, Cambodia, Kenya, Madagascar, Pakistan, Tajikistan, Tanzania, Thailand and Vietnam. You may have noticed that all of these countries are also sources of corundum. Spinel is commonly found in association with ruby and sapphire. This is another reason the two gems' identities have traditionally been confused.