Rare specimen of Dioptase crystals included in Quartz. These are not often seen and it's the only one I've ever owned. There were a handful of specimens from the Congo with slightly bigger Quartz crystals and included Dioptase crystals that sold in the $25K-$35K range. In this specimen, the Dioptase crystals settled on an earlier generation of yellow colored Quartz (which I understand is caused by Sulfur).