department gf mineralogy. 161 



Department of Mineralogy. 



Research. 



The systematic investigation and description of the 

 Mineral Collections have been in progress during the past 

 year. In the Halide Division a combined crystallographic 

 and chemical investigation has been made of the group of 

 Hornsilvers, the result of which has been to show that in 

 these minerals the chloride, bromide, and iodide of silver 

 may occur together in isomorphous combination in very 

 varying proportions ; descriptive catalogues of the specimens 

 of lodyrite and Miersite have been prepared. In the 

 Sulphide and Sulpharsenite Division, Calaverite, a telluride 

 of gold, has been the subject of a detailed crystallographic 

 study, which has thrown some light upon the difficult and 

 extraordinary problem involved in the morphology of this 

 mineral ; for the study of the facial development of the 

 crystals of Calaverite, the three-circle goniometer designed 

 and constructed for the Department in 1899 has been of great 

 service ; indeed, the research has only become practicable 

 through the existence of the instrument. An improved form 

 of this new kind of goniometer is now in process of construc- 

 tion. In the same Division a chemical investigation has 

 established the identity of Kilbrickenite and Geocronite. 



Crystallographic measurements have -been incidentally 

 made on various other species, including Dufrenoysite, 

 Baumhauerite, Rutile, Tremolite, Augite, Cassiterite, Fahlerz, 

 Barytes, Silver, Rhodonite, and also on some carbo-silicides 

 of iron and manganese. 



Petrographical examinations have been made of the rock- 

 specimens collected by the " Southern Cross " Antarctic 

 Expedition under Mr. C. E. Borchgrevink ; of Mr. M. Fergus- 

 son's collection from Lake Tanganyika, &c. ; of Sir Harry 

 Johnston's collection from British East Africa ; and of Mr. 

 Shockley's collection from Siberia. A comparative examina- 

 tion has been made of phonolitic rocks from East Africa and 

 the islands of Ascension and St. Helena. For this petro- 

 graphical work 168 thin sections of rocks have been prepared 

 and microscopically examined. 



In the Chemical Laboratory, 15 quantitative analyses have 

 been made, viz., of Calaverite (4); Basalt from Mount Terror ; 

 Kilbrickenite (2); lodiferous Embolites (5) ; Miersite (2) ; and 

 Marshite. Further, 77 doubtful minerals have been qualita- 

 tively analysed, and 17 specific gravity determinations have 

 been made. 



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