. 188. OF COMPOUND MINERALS. 2G7 



in case they should themselves be straight, while the 

 others are curved or bent. Straight lamellar particles, or 

 such as in themselves are simple, are found in prismatic Kal- 

 baryte, axotomoiis Kou phone-spar, rhombohedrai Lime-ha- 

 loide (the varieties called Slate-spar), &c. 



The size of the particles of composition varies consider- 

 ably. Sometimes they are so minute that they entirely 

 withdraw themselves from observation. Yet a compound 

 mineral, consisting of such impalpable individuals, does not 

 for that reason cease to be a compound one. This subject 

 requires our particular attention. A specimen of hexahe- 

 dral Lead-glance being given, which consists of consider- 

 ably large particles of composition, we may very easily 

 find another, in which these particles are smaller, and a 

 third, in which the size of the particles is still more dimi- 

 nished. These specimens differ only in the size of their 

 constituent individuals. We may continue, and discover a 

 fourth variety, a fifth, &c., every one of them being in a 

 similar relation to that which immediately precedes it ; 

 very soon we arrive at such varieties, whose individuals are 

 scarcely perceptible to the naked eye. Yet the immediate 

 connexion with the other varieties, and a magnifying glass, 

 demonstrate that they are all the same mineral, viz. va- 

 rieties of hexahedral Lead-glance. No reason can be as- 

 signed why these varieties should be the limit of the 

 series ; the members immediately following will be the va- 

 rieties of compact Lead-glance ; and in these very often the 

 individuals are so miitute, that they withdraw themselves 

 from observation even through a magnifying glass. Com- 

 pact Lead-glance, therefore, is not a simple mineral, but a 

 compound one. From the same point of view, we must 

 consider the compact varieties of rhombohedrai Lime-ha- 

 loide (compact Limestone), of octahedral Fluor-haloide 

 (compact Fluor), of prismatic Hal-baryte (compact Heavy- 

 spar), of rhombohedrai Quartz (Flint, Hornstone, Chryso- 

 prase, &c.), and of other species. The composition which 

 really takes place, cannot be observed only on account of 

 the minuteness of the particles of composition. 



