244 Professor Necker on Minei'alogy considered 



appearance and lustre, as well internally as externally, and at 

 the same time perfect opacity and some characteristic electrical 

 properties. On the other hand, we find that a still greater num- 

 ber of orders are composed of individuals containing either oxy- 

 gen, or fluorine, or chlorine combined with combustible sub- 

 stances, and that out of 207 genera of this description, 189 or 

 /yths are deprived of any true metallic appearance or lustre, 

 and possess transparency, or at least more or less translucidity 

 and electrical characters quite opposite to the other series of 

 genera. 



In following this indication, we ought first to divide the mi- 

 neral kingdom into two great classes ; the one class composed of 

 individuals which, with a true metallic appearance and complete 

 opacity, contain no substance supporting combustion, as oxygen, 

 fluorine, or chlorine ; the other class of individuals, destitute 

 of any metallic appearance, possessing more or less translucidity, 

 a lithoid aspect, and containing oxygen, or fluorine, or chlorine. 

 These two very natural classes will comprehend 258 out of 284, 

 which is the total number of known genera, or ibe | Jtb part of 

 the existing genera. 



Of the remaining 26 anomalous genera, 24 possess at the same 

 time something of the metallic and something of the Hthoid ap- 

 pearance, combining metallic lustre and transparency, or an 

 earthy streak and powder. Some are metal-like oxides, the others 

 are transparent bodies with some remaining metalHc lustre, that 

 do not contain any elemental supporter of combustion, being con- 

 sidered pure metallic sulphurets. Such a group, comprising 

 only the ^^th part of the existing genera, will, as an artificial 

 class, be placed between the two preceding natural ones, and re-i 

 main there until chemistry, by further investigation, shall point 

 out the cause of these anomalies. The same thing will be said of 

 the two remaining anomalous genera, which, although containing 

 no oxygen, yet being completely transparent and having a true 

 lithoid appearance, ought to be artificially, it is true, but pirovi- 

 sionally, brought near to the class of which such physical pro- 

 perties are the distinctive characters. They will be separated 

 from this class and formed into a distinct class, of which their 

 common property of being inflammable will be the distinctive 



