Identifying Bismuth Minerals

Charcoal Tests. When heated with sodium carbonate on charcoal in the reducing flame, a bismuth mineral will yield a metallic globule and an oxide coating. The metal is easily fusible, lead-gray when hot, but becomes covered with an oxide coating on cooling. It is only imperfectly malleable, for when hammered out it flattens at first but later breaks into small grains. The oxide coating, Bi₂O₃, is white with a yellow ring next the mineral. These bismuth reactions are quite similar to those for lead, consequently the following modification list useful. If the bismuth mineral is fused on charcoal with a mixture of potassium iodide, KI, and sulfur, a characteristic and distinctive coating is obtained. This sublimate is yellow next to the mineral and brilliant red on the outside. Under similar conditions with lead a solid yellow coating would be obtained.

Sublimate on Plaster Tablet. When mixed with a mixture of potassium iodide and sulfur and heated a bismuth mineral will give a sublimate that is chocolate-brown with underlying red in color. Subjected to ammonia fumes the coating becomes first orange-yellow, then red.