Spinel is a gemstone that forms on the surface of a rock or grows out of it, and a spinel can be either a single crystal or a druse (a group of small crystals growing together). Pure spinel is completely transparent like water, but natural admixtures often dye spinel into various colors. Colored spinel is found more often than the pure one. Depending on the color, the gem can be called different names: vivid green is chlor-spinel; dark green is ceylonite; red is ruby spinel; brown is pleonastic spinel; violet is almandine; blue is sapphire spinel; dark blue is ganospinel. There are also rose, orange, and yellow spinels.
Only smooth and clear spinel stones can be regarded as gems. Transparent colored spinel crystals are called noble spinel. The size of the crystals is usually small, but some crystals grow up to 28 cm (11”) high. Crystals usually weigh about 10-12 carat, but occasionally there are some larger gems found as well. For example, the unique dark red spinel in the crown of Katherine II weighs almost 400 carat. The rarest and the most valuable spinel is whit spinel coming from Sri-Lanka.
The most famous colored spinel is the Black Prince Ruby. Until the beginning of the 19th century, people could not tell the difference between red spinel and rubies, and, because large rubies were truly rare, large spinels were often called rubies and were used to decorate royal crowns. Many famous rubies, such as Catherine the Great's Ruby, the famous ruby of the British crown known as the Black Prince Ruby (170 carat), and the Timur Ruby (361 carat) turned out to be spinel. The largest spinel found is the Samarian Spinel – it weighs exactly 500 carat.
Natural ruby-spinel sometimes exceeds true rubies in shine and luminosity, but a ruby is always the more solid and durable stone. As time passes, spinel tends to lose shape, its facets go dull, and its edges go blunt and rounded. The indisputable advantage of spinel is its outstanding glitter both in natural and artificial light – that is why it is often used for adorning expensive and charming jewelry. The most valued spinels are red and sapphire spinel, then rose and violet spinels, and then black. Other colored spinels with the grayish-blue spinels as the least valued.
Like many other gems, today it is possible to produce synthetic spinel. Synthetic spinel looks like rubies (red spinel) and sapphires (ganospinel) and very often it is used in jewelry. The pure, transparent spinel is sometimes used as a substitute to diamonds, but spinel tends to lose its inner shine after being cut and looks less attractive than diamonds.
Spinel is believed to strengthen the immune system and to improve sight and blood circulation. It is a lucky stone, but it should not be worn too often because it can lose its powers or even suppress the natural powers of its owner. Occasional wearing of spinel earrings or rings can help bring luck in family life and to find one’s true love; it can also be a help in long journeys and business trips. In the Middle Ages, spinel amulets were worn by people who wanted to prolong their youth and longevity.