As a mineral specimen Color Emerald green, difficult to photograph with the digital camera. Hardness 5-5.4 Specific gravity 3.3 Dioptase is one of the few silicates to crystallize in the same symmetry class as dolomite and forms crystals that can have a typical carbonates' rhombohedral shape. Dioptase shares this symmetry with the typically ice clear silicate phenakite and the fluorescent but rarely well crystallized willemite. Specimens of dioptase are often deeply colored and show well developed crystals. The faces of the rhombohedrons, and even the prism faces, are very reflective due to a fairly high luster.
Crystals can be quite clear but at times they seem to be cloudy due to the deep color.
The special attributes of a high quality specimen of dioptase are hard to describe adequately but must be observed in person in order to appreciate their value. Fine crystals of dioptase are still available in large supplies but their sources are few and the continued demand may put a squeeze on their abundance in the future. Crystals are transparent to translucent. The crystal habits include stubby crystals that are usually well formed prisms topped with the three faces of a rhombohedon. Prisms are six sided and usually not very long.