Dioptase

Long mistaken for emerald, it wasn't until the end of the 18th century that French mineralogist René Just Haüy demonstrated that it was a mineral in its own right, more specifically a copper silicate.

The best deposits that provide a quality stone are located in the Congo, in the Democratic Republic of Congo, but also in Namibia, Angola, Kazakhstan and the State of Arizona in the United States.

It is rarely used in jewellery, and if it is, it is in its rough form, due to its low hardness.