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Description of a triple Sulphuret, of Lead, Antimony, and Copper, from 

 Cornwall ; with some Observations upon the various Modes of Attrac- 

 tion which influence the Formation of mineral Substances, and upon 

 the different Kinds of Sulphuret of Copper. By the Count de Bour- 

 non, F.R.S. and L.S. Read December 22, 1803. [Phil. Trans. 

 1804,/?. 30.] 



The copious contents of this paper are arranged under the three 

 following heads : 1 . A description of the sulphuret of lead men- 

 tioned in the title ; 2. Observations on the various modes of attrac- 

 tion which influence the formation of mineral substances ; and 3. Ob- 

 servations upon the different kinds of sulphuret of copper. 



1 . The cupro-antimonial sulphuret of lead, described in the first 

 part, has hitherto been found only in Cornwall; and though many 

 specimens of it are to be met with in various collections in the king- 

 dom, yet no writer has hitherto taken any particular notice of it, nor 

 has it been classed by any of the late compilers of mineralogical 

 systems. Mr. Hatchett is the first who, on a careful analysis, has 

 ascertained it to be a triple sulphuret, in which the sulphur is com- 

 bined with lead, antimony, and copper ; each of these ingredients 

 exhibiting their characters in so striking a manner as to afford, in 

 some measure, a new example of a natural compound in the mineral 

 kingdom. 



The following are its principal characters. It is of a dark gray 

 colour ; it has a brilliant lustre, and is very brittle ; its hardness is 

 such, that it very easily cuts calcareous spar, but is not sufficient to 

 scratch fluor spar ; it slightly marks white paper ; when rubbed, it 

 does not emit any smell ; when powdered and thrown upon a hot 

 iron, it emits a phosphorescent light ; and its specific gravity is 5765. 

 The form of its primitive crystal is a rectangular tetrahedral prism, 

 with terminal faces perpendicular to its axis ; but as no specimen 

 has yet been discovered in which the above-mentioned form is totally 

 destitute of secondary facets, the author enters into a minute investi- 

 gation of the various modifications of this form, hoping by this means 

 to promote essentially the knowledge of the crystalline character, so 

 important in the study of mineralogy. These modifications are four 

 in number, and can only be understood by inspecting the figures 

 which are subjoined to the paper. 



To these characters is added the more essential one, which is sup- 

 plied by the proportions of the constituent parts of the substance. 

 These, according to Mr. Hatchett's analysis, consist of 42'62 of 

 lead, 24-23 of antimony, 12*80 of copper, and 17 of sulphur: 1-20 

 of iron was likewise yielded in the process ; but this is thought to 

 have been a mere accidental mixture. It is next observed, that all 

 the characters in this substance indicate very plainly the mutual 

 combination of the three sulphurets of which it is found to be com- 

 posed ; the whole of the external characters above described differ- 

 ing materially from those of either of the three sulphurets, and also 

 from those of any metallic substance hitherto known ; and the pro- 



