. 190. OF COMPOUND MINERALS. 71 



nected 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 occur in hexahedral Lead-glance, 

 rhombohedral Lime-haloide, rhombohedral Quartz, &c. 



The following observations will furnish characters in 

 most cases perfectly sufficient for distinguishing mixed mi- 

 nerals and compound minerals, in both of which the par. 

 tides disappear on account of their minuteness. 



The different ingredients of the mixture are sometimes 

 found separated from the rest in more or less pure masses, 

 by which the mixture 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 en- 

 tirely disengaged, or separated from each other, as is the 

 case with rhombohedral Iron-ore, and rhombohedral Quartz, 

 in the original repositories of Iron-flint, which is an inti- 

 mate mixture of these two species. Thus we infer Basalt 

 to consist of several species of the genus Feld-spar, and 

 hemi-prismatic or paratomous Augite-spar, because Green- 

 stone and the Syenitic rocks in which the particles of mix- 

 ture have only more extension, really do consist of indi- 

 viduals of the above mentioned species, and differ from 

 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 mi- 

 nerals of which they consist, without entirely agreeing 

 with any of them, as, for instance, Iron-flint, which pos- 

 sesses some of the properties of rhombohedral Quartz, &c. 

 or they assume such properties as never occur in simple 

 minerals, as, for instance, the columnar shapes of Basalt, of 

 Porphyry, the globular concretions of Green-stone, of Sye- 

 n'te, &c., which by themselves prove those minerals to be 

 compound, even though the component individuals should 

 no longer be perceptible. 



