COMPOUND MINERALS. 99 



dimensions nearly equal, or at least not very different. In the co- 

 lumnar particles, the length is greater than both breadth and thick- 

 ness ; and in direction, they are either parallel or diverging. In the 

 lamellar particle?, the length and breadth surpass the thickness. 

 There are straight and curved lamellar particles of composition. 

 The latter are not individuals, but are composed already of them- 

 selves. Examples, of the first of these kinds, occur in Coccolite, (a 

 variety of Augite,) and Colophonite, (a variety of Garnet,) of the 

 second in Pycnile, (a variety of Topav.,) and in Arragonite; and of 

 the last in Tabular Spar, and Shi'e Spar, (A variety of Carbonate of 

 Lime.) 



The size of tbe particles of composition varies considerably. 

 Sometimes they are so minute a.s scarcely to be observable. Yet 

 minerals, in which they are discoverable with difficulty, and even 

 others in which we are unable to detect them at all, may be shown 

 to be compound minerals. This may be illustrated by a reference 

 to a series of specimens of Galena. In one of them, the particles of 

 composition shall be of such distinctness as immediately to be visi- 

 ble to the naked eye ; a second will present them smaller, and a 

 third still more diminished; a fourth, filth, &c. may be conceived 

 of, regularly decreasing; and at length, we anive at one in which 

 the naked eye fails to discover the compound character. 13ut a mi- 

 croscope rendeis it apparent. Other specimens, still more compact, 

 will exiiibit particles of compOvsition only in particular places, even 

 when observed by the micro.scrope. From these observations, we 

 cannot avoid the conclusion, that these specimens ate all varieties of 

 the same mineral, and that they differ merely in the size of their con- 

 stituent individuals. And, when we find specimens thus connected, 

 (ho3e in which the composition ceases to be observed are still to be 

 regarded as compound. 



The columnar and lamellar particles are exactly in the same case. 

 The former are very obvious in the stalactitic and re inform shapes 

 of Haematite ; but in the compact varieties of this mineral they 

 wholly disappear. Of this vanishing, and almost impalpable com- 

 position, we have good examples in the reniform and stalactitic 

 shapes of Chalcedony and Gibbsite, in whose specimens, in general, 

 we can discover no trace of composition, but others do nevertheless 

 occur, of these minerals, in which the composition is visible. 



