362 



PHYSIOGRAPHY. 



CLASS II. 



which may be separated with great facility. It should be 

 observed, however, that frequently varieties of paratomous 

 Augite-spar are called Colophohite in collections. If the 

 composition be impalpable, or the particles of a granular 

 composition so intimately connected that they cannot be 

 distinguished from each other, Allochroite is formed, a va- 

 riety which is often mechanically mixed with minerals fo- 

 reign to the species. 



2. The ingredients of dodecahedral Garnet have been 

 found as follows : 



Besides these, Colophonite contains 6-5 per cent, of mag. 

 nesia, 0-5 oxide of titanium, and 1-0 water, Allochroite 6-0 

 of carbonate of lime, Pyreneite 4-0 of water, and Pyrope 

 10*0 of magnesia and 2-0 chromic acid. In general the 

 varieties of the present species present great differences in 

 regard to their mixture, only a few of which have been in- 

 dicated above. Before the blowpipe they melt pretty uni- 

 formly without effervescence into a black globule present- 

 ing a vitreous fracture. Some varieties present a slight 

 effervescence, but finally yield the same result. The bead 

 obtained by melting is frequently attracted by the magnet. 

 3. Though dodecahedral Garnet cannot be said with pro- 

 priety to enter into the composition of rocks, it occurs in 

 many of them in grains and imbedded crystals, as in gra- 

 nite, gneiss, but particularly in mica-slate, ehlorjte-slate, 

 white-stone, serpentine, in various kinds of rocks consider- 

 ed as lava, more sparingly in limestone. Precious Gar- 

 net occurs in slaty primitive rocks ; Grossular and Py- 

 rope are found in serpentine, the latter also in other rocks, 

 through the decomposition of which it is brought inte the 



