The term dioptase refers to a mineral of the class of silicates, a subclass of cyclosilicates. Its chemical formula is CuSiO3 • H2O.
The name dioptase forged by Haüy is initially feminine. The mineral was then called copper dioptase (male), abbreviated dioptase in masculine or feminine. Today, both genres survive but the French Society of Mineralogy and Crystallography and the MNHN use the masculine, and this is also the choice made by the Government of Canada’s terminology and linguistic databank.
At the end of the eighteenth century, the German mineralogist Moritz Rudolph Ferber first became interested in this mineral. But he defines it erroneously as an emerald, and it was the French mineralogist René Just Haüy who, in 1797, proved that it was a mineral by itself and gave it the name dioptase, from the Greek dia (” Through “) and optazo (” I see “), with reference to the fact that the traces of the cleavage planes can be seen through its crystals. He will give this term the feminine kind.
The topotype is found in the Altyn-Tyube copper mine, in the Kirghese steppes (Oblys of Karaganda, Kazakhstan).
The dioptase forms transparent prismatic crystals to translucent, vitreous luster. It is emerald green to dark blue-green. Its line is green and its fracture is conchoidal. Its hardness, 5 on the Mohs scale, is average.
With the blowpipe, the dioptase does not melt but blackens by coloring the flame in green. It is soluble in nitric acid and hydrochloric acid.
Dioptase, from Tanzania