COMPOUND MINERALS. 101 



the other. In this case the whole mass will be cleavable, and the 

 whole will therefore, be a single individual, and not a composition 

 agreeably to the definition in (. 70.) Hence cleavable minerals 

 are simple ; and the want of cleavage in varieties of such species 

 as commonly allow of cleavage, is a mark of their composition; be- 

 cause here one individual assumes a situation different from that of 

 another, so that their respective faces of cleavage can have no con- 

 tinuity among one another. For this reason, compact Limestone, 

 compact Fluor, and compact Heavy Spar are not cleavable, although 

 the simple varieties of the same species may be cleaved with the 

 greatest facility. 



The same applies to the pseudomorphoses. 



Among the other characters of composition, we may mention, that 

 compound minerals in which the composition can no longer be obr 

 served, are most intimately connected in all their properties with 

 those in which it is still visible, and that commonly they possess 

 lower degrees of transparency and lustre, than simple varieties of 

 the same species. Examples illustrative of the present remark may 

 be seen among specimens of Quartz, Carbonate of Lime and Galena. 



The following observations will furnish characters in most cases 

 sufficient for distinguishing mixed and compound minerals, in both 

 of which, the particles disappear on account of their minuteness. 



The different ingredients of the mixture are sometimes found sep- 

 arated from the rest in more or less pure masses, by which the mix- 

 ture ceases to be uniform. If we find an opportunity for observing 

 mixed masses of this kind, on a larger scale, we may very often 

 find those particles entirely disengaged, or separated from each oth- 

 er, as is the case with Hydrous Oxide of Iron, and Quartz in the 

 original repositories of Iron flint , which is an intimate mixture of 

 these two species. Thus, we infer Basalt to consist of Feldspar and 

 Augite, or Hornblende, because Greenstone and the Syenitic rocks 

 in which the particles of mixture have more extension only, really 

 do consist of the above mentioned species, and differ from common 

 Basalt merely by their coarser grain. 



Moreover, the mixed minerals partly possess the properties of the 

 one, partly also those of the other, of the simple minerals of which 

 they consist, without entirely agreeing with any of them, as, for 

 instance, Iron flint, which possesses some of the properties of Quartz, 

 &c., or they assume such properties as never occur in simple min- 

 erals; as, for instance, the columnar shapes of Basalt, of Porphyry, 

 and the singular forms of Greenstone, which, by themselves, prove 



9* 



