Quarterly Crystal: Dioptase in and on Quartz
Crystals of transparent colorless rock crystal quartz play host to a wide variety of mineral inclusions, some of which are highly attractive. Due to its transparency and bright blue-green color, one of the most visually striking inclusions occasionally found in quartz is dioptase. Occurring in the oxidized zones of some copper deposits, dioptase gets its vibrant color from copper, the chemical formula of dioptase being Cu6Si6O18•6H2O.
Recently we had the opportunity to examine an unusual arrowhead-shaped, fully terminated colorless quartz crystal that was decorated on one side with a crust of numerous trigonal transparent dioptase crystals that were both in and on their host. The geographic source for the crystal shown in figure 1is Kaokoveld, Namibia. Weighing 15.65 ct and measuring 25.28 × 17.51 × 7.67 mm, this unusual example of rock crystal plays host to numerous near-surface trigonal crystals (figure 2) up to 3.0 mm in length.
The visual characteristics of the features—the trigonal micromorphology, degree of transparency, and color of the numerous inclusions—suggested dioptase; this was confirmed using laser Raman microspectrometry. The euhedral dioptase inclusions were situated on only one side of the quartz, which illustrates that they developed through directional deposition late in the quartz growth cycle.