Chlorite Group and its Alternative. . 199 



with diaspore on one side and emery on the other. Hence the 

 group AlH 2 O a is at least as likely to be found in amesite as the 

 magnesian compound MgOH. 



Still another analogy between the micas and the chlorites 

 remains to be noted. In the phengitic muscovites, in some 

 phlogopites and in the lithia micas, the ratio of silicon to oxy- 

 gen is less than 1 : 4, and often approaches 1 : 3. This varia- 

 bility, as I have shown in my paper upon " A theory of the 

 mica group,"* is easily explained by supposing an admixture 

 of molecules containing the group Si 3 8 in place of Si0 4 . 

 This equivalency is well recognized in the feldspar series ; and 

 among the micas it is forcibly emphasized by the existence of 

 Lorenzen's polylithionite, in which the group Si 3 8 replaces 

 Si0 4 entirely. Does this group occur in chlorites also? 



At the end of his discussion of the leptochlorites, Tschermak 

 dismisses a number of minerals as doubtful in character, either 

 because of unsatisfactory analyses, or uncertainty in the mate- 

 rial described. In particular he names the species grengesite, 

 hullite, melanolite and stilpnomelane, to which he adds epi- 

 chlorite. All of these minerals, together with epiphanite and 

 possibly strigovite, may be reduced to typical form by assum- 

 ing the presence of Si 3 O s . For grengesite and hullite the 

 analyses are not satisfactory, and the formulae deducible have 

 therefore no weight. Strigovite has been already explained 

 by assuming in it the group AlOH, but a reconsideration here 

 is worth noting as offering an alternative formula to that pre- 

 viously given. The formulae which I have obtained are as 

 follows : 



Stilpnomelane, ( 4Fe 2 (Si,0 8 ) 2 (FeH„0 2 ) 2 H 2 



\ +3Fe 2 (Sib 4 ) o (FeIi;0,) o H 9 

 Melanolite, j lFe 2 (Si s 8 ) 2 (FeH 2 2 ) 2 H 2 



\ + 3Fe 2 (Si0 4 ) 2 (FeH 2 0„) 2 H 2 

 Epichlorite, j lMg 2 (Si0 4 j„H 4 + lMg 2 (Si 3 8 ) 2 H 4 



\ + 3Mg i (Si0 4 ) 1 (AlH,0 1 ), 

 Strigovite, ( 3Fe,(Si0 4 ) s ( AlH a 9 ),H + 



] 8Fe 1 (SiOJ t (AlH 1 0,) 1 



/ +lFe 3 (Si 3 8 ) 2 (AlH 2 OJ 2 



Epiphanite, j Me s (Si,0 h ) a (AlH a o ) s 

 ( +3Mg 3 (Si0 4 ) 2 (AlH 2 2 ) 2 



Here we find stilpnomelane and melanolite are orthochloritic 

 in type ; epiphanite is equivalent to aphrosiderite, and the 

 other species are intermediate like most of the leptochlorites. 

 The analyses discussed are these : 



Stilpnomelane from Antwerp, 1ST. Y., by Brush. 



Melanolite, Somerville, Mass., by H. Wurtz. 



* Bulletin, U. S. Geological Survey, No. 64. 



