SULPHURET OT LEAD, COPPER, AND ANTIMOXT. 335 



place iii a second division such as appear not to agree with 

 any of those already known and classed among the species 

 properlv so called; and this division maybe subdivided at 

 pleasure, as may appear necessary for the establishment of 

 order and perspicuity. 



It is obvious, that in fact, the species existing among the Ext raneou 

 sulphuretted ores of copper being perfectly known from the Ster'tiS^Ss^ 01 

 sum of the characters essentially necessary to ascertain them, ture, but may 

 the silver, lead, antimony, arsenic, &c, which happen to jSJjJ'S^. 

 be intermingled with them, are perfectly extraneous, andrieties. 

 do not in the least alter their essential nature. These inter- 

 mingled substances once known, they may give rise to sub- 

 divisions of varieties ; but these subdivisions themselves 

 would become very numerous, if proper limits were not 

 assigned to them. In the fahlertz, for example, from the 

 great tendency it has to receive into its substance an inter- 

 mixture of a great number of others, I am persuaded, that 

 we should be obliged to make almost as many subdivisions 

 as we analysed specimens. 



A collection of minerals I lately received from Russia con- New variety. 

 vinces me, that we are yet far from knowing all the gray sul- 

 phuretted ores, of which copper forms a component part, 

 or in which it is simply interposed or accidental. Among 

 the specimens in it was one bearing the name of a 

 substance, which certainly did not belong to it; and the 

 appearance of which, differing from that of every analogous 

 substance that I recollected, particularly caught my atten- 

 tion. As this specimen affords anew and interesting variety 

 of the simple sulphurets of copper; and affords- me an op- 

 portunity of showing how we may sometimes discover, that 

 a substance is simply intermingled with another, and not 

 combined with it, a point frequently difficult to determine; 

 I will enlarge upon it for a few moments. 



This substance, which is in small separate pieces in- Described, 

 terspersed in a quartz, partly compact and partly lamellar, 

 is of a fine, close, compact grain, and of a hardness nearly 

 equal to that of fahlertz, or gray sulphuret of copper and 

 iron. Its colour is a duller gray, and its fracture is more 

 smooth. Its specific gravity is 4-554. Well assured that 

 this substance was not nickel, under the name of which it 



had 



