Identifying Antimony Minerals

1. Oxide Coating on Charcoal
   When an antimony mineral is heated in the oxidizing flame on charcoal, a heavy white coating of antimony oxide settles on the charcoal at a short distance from the mineral. The coating is readily volatile when heated.
2. Open Tube Test
   When metallic antimony or a compound of antimony with sulfur is heart in the open tube, a white powdery sublimate of antimony oxide, Sb₂O₃, forms in a ring on the inner wall of the tube, a short distance above the mineral. It is a volatile coating. If the mineral contains sulfur, as is usually the case, a second coating will form as a white powder along the bottom of the tube. It is another oxide of antimony, Sb₂O₄. It is non-volatile and is usually more conspicuous than the first.
3. Sublimate on Plaster Tablet
   Mixed with a mixture of potassium iodide and sulfur yields in the oxidizing flame an orange to red sublimate of SBI₃.