Senarmontite

Only present in antimony sulfide ores, faceted senarmontite is rare. Crystals are scarce and may only reach up to one or two carats. The only locality that produces gemmy material is at Djebel Haminate Mine in Algeria. Although fake senarmontite is not known to be on the market, buyers can distinguish this mineral by its octahedral crystals, greasy texture, and heavy specific gravity.

The annual consumption of antimony(III) oxide in the United States and Europe is approximately 10,000 and 25,000 tonnes, respectively. The main application is as flame retardant synergist in combination with halogenated materials. The combination of the halides and the antimony is key to the flame-retardant action for polymers, helping to form less flammable chars. Such flame retardants are found in electrical apparatuses, textiles, leather, and coatings. Other applications: Antimony(III) oxide is an opacifying agent for glasses, ceramics and enamels. Some specialty pigments contain antimony. Antimony(III) oxide is a useful catalyst in the production of polyethylene terephthalate (PET plastic) and the vulcanization of rubber.

The structure of Sb2O3 depends on the temperature of the sample. Dimeric Sb4O6 is the high temperature (1560 °C) gas. Sb4O6 molecules are bicyclic cages, similar to the related oxide of phosphorus(III), phosphorus trioxide. The cage structure is retained in a solid that crystallizes in a cubic habit. The Sb-O distance is 197.7 pm and the O-Sb-O angle of 95.6°. This form exists in nature as the mineral senarmontite. Above 606 °C, the more stable form is orthorhombic, consisting of pairs of -Sb-O-Sb-O- chains that are linked by oxide bridges between the Sb centers. This form exists in nature as the mineral valentinite.