DIOPTASE with CALCITE (miniature)

Dioptase is a striking mineral characterized by its vibrant emerald-green to bluish-green hue, classified as a cyclosilicate of copper. It exhibits transparency to translucency and possesses a vitreous to sub-adamantine luster. The chemical formula for dioptase is Cu6Si6O18·6H2O, with an alternative representation as CuSiO2(OH)2. It has a Mohs hardness of 5, comparable to that of tooth enamel, and a specific gravity ranging from 3.28 to 3.35. The mineral features two perfect cleavage directions and one very good cleavage direction, but it is notably fragile, necessitating careful handling. Dioptase crystallizes in a trigonal system, forming six-sided crystals that end in rhombohedra. 

This mineral is favored by collectors and is occasionally fashioned into small gemstones. Additionally, it can be ground into a pigment for artistic applications. Historically, dioptase was utilized to accentuate the eyes in the Pre-Pottery Neolithic B lime plaster statues found at 'Ain Ghazal, dating back to approximately 7200 BC. In the late 18th century, miners at the Altyn-Tyube mine in Kazakhstan mistakenly believed they had discovered an emerald deposit due to the presence of brilliant green crystals. However, the mineral's lower hardness of 5, in contrast to emerald's hardness of 8, revealed its true identity. In 1797, mineralogist Fr. René Just Haüy recognized this new mineral and named it dioptase, derived from Greek terms meaning "through" and "visible," referencing the visible internal cleavage planes in intact crystals.

Calcite is a carbonate mineral and the most stable form of calcium carbonate (CaCO3). It is widely found, especially as a key element in limestone. With a hardness rating of 3 on the Mohs scale, calcite is assessed based on its ability to be scratched. Large crystals of calcite are utilized in optical devices, while limestone, primarily made up of calcite, serves a variety of purposes.