274 Prof. Chapman on the Classification of the Silicates 



Biotite Type : — Hexagonal. 

 Biotite (hexagonal or uniaxial mica), 3RO, R 2 3 , 2Si0 3 ; 

 lepidonielane, 3RO, 3R 2 3 , 4Si0 3 . 



Talc Type : — Monoclinic. 



Talc, a?MgO, #Si0 3 ; as;almatolite ; meerschaum, MgO, SiO 3 , 

 H 2 0; schillerspar,15RO, 8Si0 3 , 12H 2 0; pyrallolite (triclinic?). 



The minerals of this type are evidently allied, as aberrant 

 members, to the augite and hornblende group ; but the physical 

 and geological characters of the talcs are quite sufficient to de- 

 mand for these compounds a distinct place in the system. In a 

 linear series, then present position seems to be the most appro- 

 priate. 



Serpentine Type : — Trimetric (?). 



Serpentine, 9M S 0, 4Si O 3 , 6H 2 0; picrosmine, 6MgO, 4Si0 3 , 

 3H 2 0; villarsite/l2(MgO, FeO, MnO), 4Si0 3 , 3H 2 0; mon- 

 radite, 12(MgO, FeO), 8Si O 3 , 3H 2 0; pyrosclerite, 12RO, 

 2A1 2 O 3 , 6Si O 3 , 9H 2 0,— vermiculite, chonikrite, kammererite 

 (varieties of pyrosclerite ?) ; spadaite, 5RO, 4Si O 3 , 4H 2 O ; kero- 

 lite, 6MgO, 4Si0 3 , 9H 2 ; antigorite, 4RO, 2Si0 3 , H 2 ; aphro- 

 dite, 3RO, 2Si0 3 , 2 (or 3) H 9 0; picrophyll, 3RO, 2Si0 3 , 2H 2 0; 

 dermatine, 3RO, 2Si0 3 , 6H 2 0; gymmte, 2RO, SiO 3 , 3H 2 0; 

 hydrophite, 2RO, SiO 3 , 3H 2 ; pimelite, RO, SiO 3 , H 2 0. 



To the above may be added the following, consisting chiefly 

 of MgO A1 2 3 or Fe 2 2 , SiO 3 , and Ii 2 in various proportions : 

 saponite, mountain cork, xylite (rockwood), pyrargillite, groppite, 

 damourite, rosellane (polyargite, &c), onkosin, metaxite, and 

 others. Very few of the members, however, of this group, and 

 of the two next in succession, can fairly claim a place in a niine- 

 ralogical system. Many, without doubt, are altered or meta- 

 moiphic products referable to some of the preceding types, or to 

 some of those which follow. If admitted, therefore, into a clas- 

 sification of minerals, they should occupy an intermediate posi- 

 tion, as in the present arrangement. 



Chlorite Type: — Hexagonal (?). 

 Chlorite (leuchtenbergite), 9RO, 2R 2 O 3 , 4Si 3 , 9H 2 (?) ; 

 thuringite, 9EO, 2R 2 3 , 4Si O 3 , 9H 2 ; epichlorite, 9RO, 

 2R 2 O 3 , 6Si O 3 , 9H 9 ; ripidolite, 9RO, 3R 2 O 3 , 4Si O 3 , 9H 2 ; 

 kammererite, 6RO, R 2 O 3 , 3Si0 3 , 6H 2 O ; stilpnomelane, 6RO, 

 R 2 3 , 6Si0 3 , 6H 2 ; ottrelite, 3RO, 2R 2 3 , 4Si0 3 , 3H 2 (?) ; 

 iberite, 3RO, 3A1 2 3 , 4Si0 3 , 3H 2 0; diphanite, 4RO,6Al 2 3 , 

 5Si O 3 , 4II 2 ; pennine, 3RO, 2R 2 O 3 , 3Si O 3 , 2H 2 O ; cron- 

 stedite, 3RO, R 2 O 3 , Si O 3 , 3II 2 ; xanthophylhte (clintonite), 

 4RO, R 2 3 , SiO 3 , IPO ; disterrite (brandisite), 7RO, 4R 2 3 , 



