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Gahnite (Zinc Spinel)

Historical Information

Gahnite is a zinc-spinet (ZnAl2O4) which was named for F. G. Gahn (1745 - 1818), the Swedish chemist. It is a member of the spinel group; when all the magnesium in spinet's composition is replaced by zinc, the mineral is then Gahnite (zinc aluminum oxide),  so sometimes called zinc spinel. With increased property values (both the refractive index and specific gravity are higher than spinet's). Gahnite has been made synthetically with the following properties: R.I. 1.82; Hardness 7 1/2; S.G. 4.6.

Color ranges of Gahnite are from yellow to green, brown and greenish black. Gahnite crystallizes in the cubic system and generally forms in the octahedral habit. Usually Gahnite is too dark in color to be effective as a gemstone, but occasionally some very nice green specimens appear.

The source of faceted Gahnite material in the past is not certain, although it was probably Brazil. Very recently, rough material of a nice peridot green from Brazil has appeared.