56 MM. Deville and Troost on-some Artificial Minerals. 



about 150 kilogrammes of Saxon lepidolite, a product was 

 obtained on the first treatment with bichloride of platinum 

 which showed the violet lines between SrS and K/3 in the most 

 intense manner, but not a trace of the lines Csa. If this plati- 

 num double salt obtained from lepidolite had been a mixture, 

 the blue line Csa must have been visible, together with the 

 violet ones ; for with the product obtained from the Dtirckheim 

 mineral water, on increasing the quantity of chloride of potas- 

 sium the violet lines always disappear first, but the caesium lines 

 much later, and indeed only with a great excess of the potassium 

 salt. Hence, besides potassium, sodium, lithium, and caesium 

 there must be a fifth alkali metal, which is present in small 

 quantities in Diirckheim, Kreuznach and other similar mineral 

 springs, but in lepidolite in larger quantity. 



M. Ste.-Claire Deville and Troost, in continuation of their in- 

 vestigation on the reproduction of the natural minerals, have 

 described the preparation of some sulphurets*. 



Sulphuret of zinc is very easily prepared by melting together 

 equal parts of sulphate of zinc, of fluoride of calcium, and of 

 sulphide of barium. A fusible gangue of sulphate of baryta and 

 of fluoride of calcium is obtained, in which are found beautiful 

 crystals of sulphuret of zinc, either imbedded or arranged in 

 geodes. Analysis proved them to be identical in composition 

 with the natural blende; but they have an entirely different 

 form. Instead of belonging to the monometric system, they 

 crystallize in a regular double hexagonal prism, which is pre- 

 cisely the form of the crystals of sulphuret of cadmium. This 

 singular observation supplies a link in the analogies of sulphur 

 and cadmium, and establishes the dimorphism of sulphuret of 

 zinc. It has received a timely confirmation in a discovery 

 which Friedel has madef of the existence of a natural sulphide 

 of zinc which crystallizes in the hexagonal system. On exa- 

 mining an argentiferous antimonio-sulphide of lead, he found 

 imbedded certain crystals which had all the chemical reactions 

 and composition of ordinary zinc blende, but was entirely dif- 

 ferent in crystalline form. The crystals consisted of a double 

 hexagonal pyramid, with occasionally the faces of the hexagonal 

 prism. These faces are strongly striated parallel to the base, 

 and the angle between the adjacent faces of the pyramid was 

 found to be about 129°, which is very near that of one of the 

 pyramids of Greenockite. It has four easy cleavages parallel to 

 the base and to the faces of the hexagonal prism. Its action on 

 polarized light further establishes the crystalline form of the 



* Comptes Rendu*, May 6, 1SG1. f Ibid. May 13. 



