MINERALOGY. 



83 



Of both these minerals, there are crystallised specimens from Corn- 

 wall; and massive pieces from Tuscany are seen in the glazed ends of 

 Cases 5 and 6. 



The rare mineral, Sternbergite, consisting of Iron, Sulphur, and 

 Silver, belongs also to this class; while Linnreite, or" Cobalt-pyrites," 

 (Co 2 S a , CoS,) is a sulphur-compound of Cobalt, exactly analogous to 

 the oxygen-compounds termed the " magnetic oxides" of Iron or 

 Manganese. Tin-pyrites is a dibasic cuprous sulphostannate, contain- 

 ing Iron and Zinc. 



The largest class of the sulphur salts is that consisting of sulph- Cases 

 arsenites, sulpho-bismuthites, and sulph-antimonites. Among these 7 & 8. 

 Tetrahedrite (Fahlerz or Grey Copper ore) is noticeable as a most 

 important ore of Copper. It is a tetra-basic sulph-antimonite of that 

 metal, in which the copper is frequently replaced by small quantities 

 of silver, and is also associated with sulphides of Iron and Zinc. In 

 some of its varieties, as in Tennantite, the Antimony trisulphide 

 is entirely, and in others partially, replaced by an equivalent of Arsenic 

 trisulphide. The argentiferous Tetrahedrite is a valuable ore of 

 Silver. Remarkable specimens of Bournonite, a tri-basic sulph-anti- 

 monite of Copper and Lead from the Herod's-foot mine in Cornwall, 

 are here in juxtaposition with those from the Hartz, and from Traver- 

 sella. The so-called Red Silvers, a group of isomorphous rhombohedral 

 minerals, are the tri-basic sulphantimonite arid sulpharsenite of Silver, 

 Pyrargyrite and Proustite ; sometimes in a comparatively isolated 

 state, but more frequently blended together in various proportions. 

 Beautiful as well for their forms as for their blood-red colours, that 

 are deeper in tint according as the antimony preponderates over 

 arsenic, they constitute one of the more precious of the ores of Silver, 

 The specimens of Pyrargyrite and Proustite exhibited in Case 8, and 

 in particular those of the latter mineral from Chili, are extremely 

 fine. 



Among these a large mass of resplendent crystals, of a rich ruby 

 colour by transmitted light, was presented by the late H. Ludlam, Esq., 

 and is a unique specimen. 



Among the rarer minerals, attention may be called to the fine 

 specimens of a variety of Freieslebenite, from Hiendelencina, in 

 Spain; also to Eireblende and Xanthocone, the latter containing a 

 tri-basic sulpharsenate and sulpharsenite of Silver; and to the series 

 of minerals from the Binnenthal, including very fine crystals of 

 Jordanite. 



Division III. Compounds of the Halogen Elements. 



(11 - u This next principal division of the Collection is also subdivided into 

 le ' the simpler compounds, and a more complex section of Salts. Among 

 m, the former will rank Calomel, Salammoniac, Common Salt (Sodium 

 chloiide), and Sylvine, the corresponding potassium chloride, the two 

 latter being crystallised in large cubes and cubo-octahedra. With 

 these are arranged the chloride, iodide and bromide of Silver, and 



