Compositions of silver halides from the Broken Hill district, New South Wales

Some 320 specimens of silver halides from the Broken Hill field, New South Wales, held in the collections of the Australian Museum have been examined. On the basis of colour and habit variations, 42 specimens were selected for analysis. Contrary to previous suggestions, compositions of individual specimens are highly variable and reflect a complex crystallisation history. Bromargyrite has been detected for the first time away from the Broken Hill main lode horizon. Compositions are discussed in terms of the lacunar nature of the appropriate phase diagrams; natural material is shown to reflect compositions of synthetic phases prepared at about 25°C. No obvious relationship between composition and physical properties could be detected for the chlorargyrite-bromargyrite series. This highlights the difficulties of visual identifications.