- Magnesium Spinel containing traces of iron, which gives it a dark green to black color.
- Grass green variety Magnesium Spinel with the color caused by traces of iron and copper.
- Zinc-rich end-member of the Spinel mineral series. Gahnite is scientifically recognized as an individual mineral species.
- Manganese-rich end-member of the Spinel mineral series. Galaxite is
scientifically recognized as an individual mineral species.
- Iron-rich end-member of the Spinel mineral series. Hercynite is
scientifically recognized as an individual mineral species.
- Chromium and magnesium-rich variety of Hercynite; may also describe brown Spinel.
- Opaque, dark blue or green to black variety of Spinel.
- Yellow to orange variety of Spinel.
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Spinel is a rare mineral, and its color and qualities make it very well substituted as a gemstone. It is cut into all gemstone cuts, especially round and oval cuts, though it is surprisingly not extensively used in demand for jewelry.
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Most gem grade Spinel comes from Mogok, Burma (Myanmar). Another important producer is Sri Lanka, especially at Ratnapura. The original Spinel gems came from Afghanistan, at Badakhshan; newer Afghan localities have recently been exploited in Jegdalek, in Sarobi. A very significant recent producer of Spinel is Luc Yen, in Yenbai Province, Vietnam. The Hunza Valley, Gilgit, Pakistan produces a nice blue Spinel. A famous occurrence of black Spinel crystals and clusters is the Aldan Shield, Yakutia, Siberia, Russia; and transparent purple crystals have come from Kukh-i-Lal, Pamir Mts, Tajikistan.
Madagascar also has several notable localities in Tulear Province, especially at Ambatomainty, where large clusters of black crystals have occurred. Tanzania also has noted occurrences in Ipanko and Morogoro. A European location of note is the Fassa Valley (Val D'Fassa), Trento Province, Italy. Spinel has been found in Canada, in Ross Township, Renfrew Co., Ontario; and in the Parker mine, Notre-Dame-du-Laus, Quebec.
In the U.S., the finest crystals came from the Franklin Marble region which stretches from Sussex Co., New Jersey to Orange Co., New York. Classic Spinel localities in that region in New Jersey include the Limecrest Quarry, Sparta; the Sterling Hill Mine, Ogdensburg; and Franklin, Sussex Co. In New York, they include Amity, Edenville, and Warwick, Orange Co. Amity is perhaps the finest U.S. occurrence, where enormous black octahedrons were found in the 18th century. Enormous Spinel crystals were also found in a lost locality in Monroe, Orange Co., New York. Spinel was also found at Bolton, Worcester Co., Massachusetts, and opaque blue crystal clusters occur near Helena, Lewis and Clark Co., Montana.
In the U.S., Gahnite has come from Franklin and Ogdensburg, Sussex Co., New Jersey; the Mt. Apatite District, Auburn, Androscoggin Co., Maine; and the Davis Mine, Rowe, Franklin Co., Massachusetts.
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Corundum var. Ruby - Harder (9), different crystal form.
Magnetite - Softer (5½ - 6½), strongly attracted to magnets.
Franklinite - Softer (5½ - 6½), slightly attracted to magnets.
Zircon - Different crystal forms.
Chromite - Softer (5½), heavier (4.1 - 5.0).
Garnet - Different crystal forms.
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