Description
In mineralogy, spinel refers to a group of similar minerals, only a few of which are gemstone-quality. The origin of the name is unclear, possibly from the Greek for spark or the Latin spina, meaning arrow. The coloring agents are iron, chromium, vanadium, and cobalt. Large stones are rare, and star spinels are very rare. The structure of spinel consists of 32 oxygen atoms and 24 cations. Eight of the cations have a 4-ring (tetrahedral positions), and 16 have a 6-ring (octahedral positions). There are two structurally different types: the normal spinel structure and the inverse spinel structure. In the normal spinel structure, the distribution of cations over the tetrahedral and octahedral positions is as follows: 8 R2+ in tetrahedral positions, 16 R3+ in octahedral positions. In the inverse spinel structure, the distribution is: 8 R3+ in tetrahedral positions, and 8 R3+ and 8 R2+ in octahedral positions. Spinels have been called carbuncle stones since antiquity, along with other stones. The current name arose later. As can be seen in numerous pieces of jewelry, spinel was once highly prized. However, initially, for example, in the English crown jewels, spinel was considered a ruby. In the past, spinels were mainly found in gemstone deposits in Burma and Sri Lanka. Some exhibit a cat's-eye effect. Spinel is difficult to distinguish from ruby due to its color. Gemstone-quality spinels are found in Thailand, Cambodia, and Laos. Localities in India and Australia are less important. Spinels have been found in Africa, in Madagascar, and in Kenya. Recently, spinels have also been found in Pakistan and Afghanistan. Gemstone-quality spinel is also known from Brazil. In the United States, it is found primarily in California, Montana, New York, New Jersey, Virginia, and North Carolina. In Canada, crystals up to 5 cm in size have been found in the marble of Glancoe. Spinels also occur in Ontario and Tajikistan. The pure, pink-colored cut stones sometimes reach a weight of 100 carats. In 1986, a spinel weighing 5.1 kilograms was found. In Europe, spinels are found in Norway, Finland, Italy, and Germany. Spinels were frequently used in crown jewels. The most famous is probably the 398.5-carat dark red spinel in the Russian Imperial Crown in the Moscow Armory. The British Crown also contains two large spinels, the so-called Black Prince Ruby of 170 carats and the Timur Ruby of 361 carats. The Crown of St. Wenzel in Prague also contains large spinels, a total of 45. The British Museum in London holds two spinels weighing 355 and 520 carats, respectively.
Gemstone therapy Spinel (all colors)
