Chlorite Group and its Alternative. 193 



Pennine, Sp s At 2 to SpAt 



Clinochlore, SpAt to Sp 2 At 3 



Prochlorite, Sp 2 At 3 to Sp 3 At 7 



Corundophilite, Sp 3 At 7 to SpAt 4 



Transforming these expressions, and, for brevity, writing 

 A1H 2 2 = A, and MgOH = M, we have : 



Sp 3 At 2 = Mg B (Si0 4 ) 8 . A 4 M 6 H 7 = n Mg 2 (Si0 4 ) 2 R' 4 



SpAt = Mg 3 (Si0 4 ), . A 2 M 2 H 2 = 



Sp 2 At 3 = Mg,(SiOj; . A 6 M 5 H 3 = 



Sp.At, = Mg 13 (SiO 4 ) ]3 .A 14 M 10 H 2 = 



SpAt 4 = appproximate agreement only. 



In the last case, corundophilite, Tschermak's formula agrees 

 better with the actual analyses than any formula derived from 

 my system. The cause of divergence will be considered in 

 connection with the structure of amesite, later. Although the 

 difference is small it ought not to be ignored. 



In general, then, the orthochlorites may be provisionally 

 regarded as mixtures of the three typical or generic salts Mg 2 

 (Si0 4 ) 2 A 4 , Mg 2 (Si0 4 ) 2 M 4 , and Mg 2 (Si0 4 ) 2 H 4 . Whether these 

 -compounds exist separately in the mineral kingdom is an open 

 question, and one not easy to answer. To each of them there 

 are approximations ; ekmannite for example is near Fe„(Si0 4 ) 2 

 H 4 in composition ; but it is more probable that the chlorites 

 proper are mixtures of intermediate salts. Some pennines, for 

 instance, fall near the compound Mg 2 (Si0 4 ) 2 AMH 2 ; and other 

 like substances appear among the minerals which Tschermak 

 places in the subgroup of leptochlorites. A consideration of 

 the latter must precede further discussion of theory. 



According to Tschermak, the leptochlorites form three sub- 

 groups, as follows : 



I. Daphnite, At 5 At' 5 Sp 



Chamosite, At 3 At' 3 Sp 



II. Metachlorite, At 6 St 2 Sp 3 



Klementite, At 4 St 2 Sp 



Cronstedtite, AtS 4 t 



Thuringite, AtSt 



Euralite, _ At 3 St 4 



Strigovite, St 



III. Diabantite, Ct 4 Sp 7 



Aphrosiderite, Ct G At 6 Sp 4 to Ct 3 At t Sp 4 



Delessite, Ct a At„Sp 5 to CtSp 



Rumpfite, Ct 4 At'' 4 Sp 



Epichlorite, grengesite, melanolite, etc., he regards as chlo- 

 rites, but as not yet definable. The delessite from Friedrichs 

 roda he places provisionally in the first division of the lepto- 

 chlorites, along with daphnite and chamosite. The formulae 

 given are deduced from specific analyses, but when several 



