Black chalcedony onyx in the rough is from Africa. Stock #403. Large rough will weigh from 10-20 pounds each, and smaller rough may be saw blocked from 2 pounds and up. This popular semi-precious gemstone is great for classic color jewelry, as a base for items of interest for display, and or used as a base for opal cabochons, which will brighten the colors of the opal. The image shows a black chalcedony onyx slab.