156 accounts, etc., of the british museum. 



Department of Mineralogy. 



Research. 



The systematic investigation and description of the 

 Mineral Collections have been continued during the past 

 year. 



In this connection, in the Sulpharsenite and Sulphanti- 

 monite Class, a crystallographic and chemical research has 

 been made on Binnite and Tetrahedrite, the result of which 

 has been to establish the specific identity of Binnite and 

 Tennantite, and to provide for the whole Fahlerz group of 

 minerals a new general chemical formula explanatory of the 

 way in which iron and zinc enter into the composition of 

 these minerals. This investigation has involved the measure- 

 ment of many crystals of Binnite and Tetrahedrite, the 

 careful picking out under the microscope of absolutely pure 

 material for analysis, and the determination of the specific 

 gravity and the quantitative chemical analysis of the material 

 so selected. 



In the Haloid Division, the species Laurionite, Calomel, 

 and Fluor have been more especially under investigation. 

 Many crystals have been goniometrically determined, exactly 

 orientated sections have been ground and optically examined, 

 and a new species of the division, Paralaurionite, an oxy- 

 chloride of lead, has been recognised and described. In order 

 to expedite investigation of this character, additional fittings 

 have been devised for the conversion of one of the instru- 

 ments into a three-circle goniometer ; the accuracy and 

 efficiency ^of the adjustments of this new instrument have 

 been thoroughly tested. 



A collection of mineral specimens, brought from Bolivia by 

 Sir Martin Conway and presented by him to the Trustees, 

 has been examined and determined, and a detailed report 

 prepared. Complex twinned crystals of the very rarely 

 crystallised mineral Stannite found in this collection have 

 been investigated, and two quantitative chemical analyses 

 have been made, the result of which has been to establish 

 more firmly the formula already hesitatingly accepted for 

 that mineral. 



A chemical and crystallographic investigation has been 

 made of Florencite, a new hydrated phosphate of alumina 

 and cerium earths discovered by Dr. Hussak in Brazil. The 

 mineral has been shown to be isomorphous with another 

 species, the recently described Hamlinite, the barium and 

 strontium of the latter being replaced in Florencite by 

 cerium earths. 



Crystals of the following species have been incidentally 

 measured : — Albite, Anatase, Andorite, Anglesite, Anorthite, 

 Argyrodite, Augelite, Augite, Axinite, Barytes, Blende, 

 Brookite, Calcite, Cassiterite, Churchite, Columbite, Copper 

 Pyrites, Dolomite, Epidote, Heulandite, Idocrase, Ilvaite, Iron 



