Chlorite Group and its Alternative. 191 



Serpentine, Sp. MgSi a O, . H a . (MgOH) a 



Amesite, At. Al 2 Si0 7 . H 2 . (MgOH) g 



" 1st deriv., At'. Al 2 Si0 7 . H 3 . MgOH 



2d " At". Al 2 Si0 7 . H 4 



Strigovite, St. SiO„ . Al 2 SiG 7 . H a . (MgOH) a 



Chloritoid, Ct. Al a Si0 7 . H a . Mg 



Of these compounds, four are represented by known 

 minerals ; although the amesite and strigovite formulae rest 

 each upon a single analysis. Two, the molecules At' and 

 At", are hypothetical. Empirically, all the chlorites of 

 well established character correspond in composition to mix- 

 tures of these six molecules ; but a few of the allied minerals, 

 such as epichlorite and stilpnomelane, are unaccounted for. 

 The latter are yet to be brought into line. 



At a first glance the six molecules, as just written, appear to 

 be remarkably alike in form. But when they are written 

 structurally, as Tschermak himself writes them, they become 

 somewhat dissimilar. Serpentine is then represented as a salt 

 of the acid H 6 Si 2 7 . Amesite, with its two derivatives and 

 chloritoid, appear as basic orthosilicates. Strigovite is given as 

 a salt of the acid H 4 Si 2 6 . That is, three different silicic acids 

 are involved in Tschermak's theory, and the first apparent- 

 simplicity of the scheme disappears. All of the six molecules, 

 however, with the single exception of the non aluminous ser- 

 pentine, are supposed to contain the structural nucleus 



-O. O-Al-O- 



X >o 



_O x \0-Al-0- 



to which the remarkable similarities of the chlorites may be 

 due. Through chloritoid the chlorites become affiliated with 

 the clintonite group ; but with the micas, at least as the latter 

 have been interpreted by Tschermak hitherto, no special anal- 

 ogies of structure appear. 



Now, admitting that Tschermak's theory accounts for the 

 known facts as fully as he believes, the question arises whether 

 his mode of interpretation is the only one possible. If it is, 

 then the problem of the^ chlorite group is solved, and contro- 

 versy is out of court. But if other schemes can be devised, 

 representing the facts equally well, further investigation be- 

 comes necessary. Pending the acquirement of new experi- 

 mental evidence, we may discuss rival systems upon philo- 

 sophic grounds ; and that which is simplest, most general, and 

 best supported by analogies, should have preference. Ulti- 

 mately, of course, the problem must be attacked by means of 

 experiment ; through which alone the questions at issue can be 

 finally settled. 



