At first glance, because of the vivid color and the size of the piece, most people would think this to be a Tsumeb Mine dioptase. And it DOES look the part, except for the darker matrix association, indicative of Reneville, in the Republic of Congo (not to be confused with the Democratic Republic of Congo!) The crystals are just a bit more translucent in the "skin," and the overall look is not quite "Tsumeby"... but it is close to what those far pricier classics look like. It is in fact from Reneville (plancheite on backside is indicative, for one, as well as the darker matrixy bits on the left), and is probably older than the mid-1980s Tsumeb material of the same species, which fetch such a premium in part just because they are from the more famous mine locale. The crystals are sharp and there are many discrete crystals poking up, to over 1 cm. The color saturation is the best for the locality, a very vibrant hue which has some "life " to it and not so dark as to suck up too much light and color, as is sometimes the case.