Dioptase

In the 18th century, the German mineralogist Moritz Rudolph Ferber became interested in and studied this mineral, which he considered (erroneously) to be emerald. In 1797, the French mineralogist René Just Haüy demonstrated that it was a separate mineral. It is a copper silicate.

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