Dioptase was originally given the name kupfersmaragd meaning copper emerald . The reason being that, in the 18 th century, dioptase was often mistaken for emerald , as both minerals share a similar green colour. Dioptase , however, is softer and more brittle than emerald , and although it also makes a good quality gemstone, it is rarely used in jewelry. As a result, dioptase's value as an ornament is highly prized. The dominant colour in dioptase is emerald green, but in some cases, the mineral may have a bluish tint. In viewing dioptase crystals from the axis one will notice that they appear darker, than from the side. Hence, they are termed dichroic and cutting techniques can enhance this phenomenon. The crystals are normally transparent , but have dark prismatic faces that may seem almost black.

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