,63 



ness, consequently, is 5,5. No true cleavage has been ascer- 

 tained. Occasionally an exfoliation is observable on the octa- 

 hedral faces, but it is always quite superficial and probably of 

 secondary origin. The fracture is splintery or subconchoidal. 



The colour of chalcolamprite is a dark greyish brown 

 distinctly inclining to red. The powder is ash-grey. The 

 crystal faces exhibit a very characteristical metallic lustre with 

 iridescence in copper -red and green i hence the name of the 

 mineral). On the fracture the mineral shows a marked greasy 

 lustre. It is opaque; only in thinnest splinters translucent. 



A microscopical section thin enough to be translucent has 

 a straw-yellow colour and is optically perfectly isotropic. It is 

 traversed by fine irregular cracks; and the mineral contains a 

 large number of microscopical inclusions, the nature of which 

 could not be determined. A section oriented parallel to an 

 octahedral face shows a feeble indication of zonal structure 

 parallel to the triangular outline of the section. The zones 

 consist of alternating lighter and darker substance. 



By weighing in benzole the specific gravity of chalcolam- 

 prite was found to be 3,77 (Mauzelius). 



As chalcolamprite , as well as the following mineral 

 (endeiolite), had on a preparatory examination proved to be 

 mainly niobates, which, together with their crystalline form and 

 other properties indicated that the composition of the minerals 

 ought to be about that of pyrochlore, the scanty amount of 

 material of each mineral available for analysis was divided into 

 two portions, one for the determination of fluorine and water 

 and the other for the determination of the other constituents. 

 The latter was decomposed by hydrofluoric and sulphuric acids. 

 The two minerals were analyzed at the same time and by the 

 same methods, and showed a great agreement in composition. 

 In both analyses there was a loss of about 10 per cent. The 

 method of analysis was such as made it necessary to infer that 

 this loss could only be silicic acid. Fortunately, another portion 



ir 



