Spinel

True Spinel has long been found in the gemstone-bearing gravel of Sri Lanka and in limestones of Myanmar and also in Thailand.

Colour and Value

Spinel is a very attractive and also has historically important gemstone mineral. Its typical red color, although pinker, rivals the color of ruby. In fact, many rubies, of notable fame belonging to the crown jewel collections, were found to actually be Spinel. Perhaps the greatest mistake is its Black Prince's Ruby set in the British Imperial State Crown. Whether this mistake was accidents or clever substitutions of precious rubies for its less valuable Spinel by risk taking jewelers, history is unclear. The misidentification is meaningless in terms of the value of these gems for even Spinel carries quite considerable amount of worth and these stones are actually priceless based on their history, let alone their carat weight and pedigree.

Today, expensive rubies are still substituted for its Spinel in much the same way a diamond is substituted by the cubic zirconia. Not to commit a fraud and theft but to prevent one. Spinel can take the place of a ruby that would have been displayed in public by an owner who is insecure about their rubies safety. The Spinel probably is still valuable but better to lose a $110,000 dollar Spinel than a $2 million dollar ruby!

Spinel and ruby are chemically similar. Spinel is magnesium aluminum oxide and ruby is aluminum oxide. This is probably why the two are similar in of its few properties. Not surprisingly, the red coloring agent in both gems is the same element, chromium. Spinel and Ruby also have a very similar luster (refractive index), density and hardness.

Spinel can be the poorer cousin of ruby, but its pinker color and other qualities make it attractive in the own right. Spinel typically forms in well formed octahedrons. But it is famous for its type of twinning that bears its name, the Spinel Twin Law. Spinel Law twinning is also found in all other isometric minerals such as diamond, galena, cristobalite, magnetite, franklinite and also other members of the Spinel group. This type of twinning produces a twin plane that is parallel to one of the octahedral faces. The plane acts as a mirror plane and produces a left and right side that are mirror images of each other. This can not sound all that spectacular for a very symmetrical mineral like Spinel which is loaded with the mirror planes. However this mirror plane is not parallel to any of the others and actually lowers the symmetry of the crystal (only in appearances though).