Spinel is commonly found in alluvial gravels with corundum and also in association with with gneiss, serpentine, calcite, dolomite, and garnet. Found in Burma, Sri Lanka, Afghanistan, Tadjikstan, and East Africa, the mineral spinel is found in a large variety of colors including orange, pink, black, blue, lavender, mauve and vivid red.
With a hardness of 8 and no cleavage planes, spinel is a tough and durable gemstone suitable for any kind of jewelry. Its’ luster is vitreous and rough crystals can be transparent, translucent or nearly opaque. A member of the isometric system, the octahedron is the typical habit. Dodecahedrons and combinations of other isometric forms are also common. Many crystals are twinned on the plane of the octahedral face forming flattened triangular forms known as “spinel twins”.
Precious spinels appear strikingly clean and free of inclusions. This impression is due among other things to the lack of liquid inclusions. The best proof of spinel is spinel and microscopic octahedra may be scattered in long chains and sinuous bands throughout inner stretches of the host crystal. Besides these mini spinels, spinel shelters a whole range of other guest minerals including albite, anhydrite, apatite, baddeleyite, calcite, olivine, and titanite.
The spinels are a group of oxides that have very similar structures. The spinel group contains over twenty members, but only a few are considered common. Named after their main gemstone representative, spinel, this is an important group of minerals. Spinel is an aluminate of magnesium, MgAl2O4 in which magnesium may be replaced by a ferrous iron or manganese, and aluminum by ferric iron or chromium. Gem spinel is just one of an isometric series in which the magnesium may be wholly replaced by ferrous iron or zinc or partly replaced by manganese and ferrous iron. Other varieties closely associated with spinel include Gahnospinel (dark green) (Mg,Zn)Al2O4; gahnite (blue, dark blue) ZnAl2O4; hercynite (dark to black) FeAl2O4; ceylonite (dark colors) MgFeAl2O4; picotite (dark green to black) Fe(Al,Cr)2O4; and galaxite (dark red to black) MgAl2O4; Other members of the spinel group include magnetite (Fe3O4); and chromite (Fr Cr2O4). There are a number of other minerals which are replacements for the double oxides.
Perhaps the most famous spinel is the Black Prince's Ruby, a magnificent 170-carat red spinel that currently adorns the Imperial State Crown in the British Crown Jewels. This stone, one of the most famous in the world, is the Black Prince's Ruby. As large as a hen's egg, weighing approximately 170 carats, and measuring five centimeters in length, the Black Prince's Ruby is a spectacular red that seems to glow with an internal fire of its own. It is so remarkable that it has become one of the world's most cherished jewels. The Black Prince's Ruby really isn't a ruby at all, it's actually a spinel, and it has a long and fascinating history.
The gem's first known owner was Abu Said, a Moorish prince of Granada in Spain in the mid-1300s. Abu Said lost the gem, as well as his crown and his life, to Don Pedro the Cruel of Seville. In 1366 Don Pedro's own brother attacked him in turn, but Don Pedro successfully defended himself with help from the armies of the Black Prince of Bordeaux. As payment, the Black Prince demanded Don Pedro's prize jewel, and Don Pedro was in no position to argue.
How the Black Prince's Ruby came to England is unknown, but it made its next historical appearance in a jeweled helmet worn by the English king, Henry V, at the Battle of Agincourt in 1415. The helmet saved Henry's life when a blow from the battleaxe of the French duke of Alencon nearly destroyed it. Both the king and the helmet survived the war, and the Black Prince's Ruby remained in English hands. Later, King James the First had the gem set into the state crown, and, despite many threats of theft, fire, and even Nazi bombs, the Black Prince's Ruby has remained the magnificent centerpiece of the British royal regalia.
While the Black Prince's Ruby is by far the world's most famous red spinel, it is definitely not the only one ever possessed or coveted by kings, queens, and emperors. The Timur Ruby, also in the Crown Jewels of England, is even larger, weighing 361 carats. It is inscribed with the names of six of its former owners.
The Kremlin Museum in Moscow has another giant gem that probably belonged to the Tsar - this one weighs 414 carats.
The most dazzling collection of fine red spinels is found in the Crown Jewels of Iran. The majority were plundered from India when the Mogul Empire fell. The largest one weighs about 500 carats, and it is indeed the biggest on record. Many others weigh over 100 carats, and more than a dozen have been carved with the name of Jahangir, a Mogul emperor over 350 years ago.
Despite its fame in the ancient world, red spinel has never been as abundant as ruby, and today it is quite difficult to find. The old mines in Afghanistan that produced so many of the giant stones in the Moguls' collections seem to have been worked out, and the gem gravels of Sri Lanka and Africa, which provide us with many beautiful pastel colored spinels, rarely contain gems with the pure intense red color of the Black Prince's Ruby.
Spinel is thought to protect the owner from harm, to reconcile differences, and to soothe away sadness. However, the strongest reasons for buying a Spinel is its rich, brilliant array of colors in conjunction with its surprising affordability.