156 ACCOUNTS, ETC., OF THE BRITISH MUSEUM. 



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 the study of the iodides of 

 silver, lodyrite and Miersite, and also of Marshite, has been 

 continued ; and the descriptive catalogue of the large series 

 of Fluor specimens has been in course of preparation. In 

 the Phosphates a study has been made of the chemical 

 and crystallographic relations of the minerals Hamlinite, 

 Florencite, Plumbogummite, Beudantite, and Svanbergite, 

 and as a result it has been discovered that these chemically 

 complex and apparently unrelated minerals belong to a 

 natural group. In the Sulphide Division the crystallographic 

 investigation of the extremely complicated twin-growths of 

 the rarely crystallised mineral Stannite has been continued, 

 and a descriptive catalogue of the specimens of that mineral 

 has been prepared. 



Consideration has been given to a general method of 

 determination of the principal indices of refraction in the 

 case of those minerals of which the indices are too high for 

 determination by the total-reflectometer : in this connection, 

 experiments have been made with the mineral Axinite, and 

 designs have been prepared for an instrument suited to the 

 determination of the refractive indices of minerals from 

 observations made in media more highly refractive than air. 



Petrographical examinations have been made of the rock- 

 specimens collected by Professor .1. W. Gregory in Tropical 

 East Africa ; of ^girine and Riebeckite-Anorthoclase rocks 

 belonging to the Grorudite-Tinguaite series from the neigh- 

 bourhood of Adowa and Axum, Abyssinia, of Tinguaites and 

 Phonolites from Elfdalen, Nassau, and the Canary Islands, 

 and of basaltic rocks from Gebel Ahmed Agar, White Nile. 

 In this connection 168 thin sections of rocks have been 

 prepared, microscopically examined, and entered in the 

 slip-catalogue. 



In the Chemical Laboratory, quantitative analyses have 

 been made of Grorudite, Lindoite, Paisanite, Solvsbergite, 

 Tinguaite, and Pitchstone from Abyssinia ; Tinguaite from 

 Elfdalen, and of a fibrous specimen of the rare Zirconia 

 mineral, Baddeleyite. The examination and quantitative 

 analysis of the Meteoric Stones which fell at Mount Zomba 

 in British Central Africa on 25th January 1899 have been 

 completed, and a report prepared for the printer. Further, 

 33 doubtful minerals have been qualitatively analysed, and 

 many specific gravity determinations have been made. 





