CHLORITE GROUP. 345 



Chloritoid and ottrelite both occur in the slates, schists, and gneisses 

 which are derived from the argillaceous sediments as a product of or 

 connected with deep-seated, and especially- deep-seated regional metamor- 

 phism, and often contact action. They are thus heavy minerals which 

 develop from the simpler constituents in the argillaceous sediments in the 

 zone of anamorphism, their formation resulting in condensation. 



Alterations. — The only alteration of the clintonite group recorded is that 

 of margarite to dudleyite. However, as no definite formula for this mineral 

 is given, it is not practicable to write an equation representing the 

 tran sform ation. 



While no other alterations of the clintonite group are mentioned, there 

 is no doubt that in the upper zone of metamorphism, especially in the belt 

 of weathering, the chloritoids, ottrelite, and margarite are decomposed into 

 simpler compounds, as are the other silicates. 



CHLORITE GROUP. 

 AMESITE, CORVXDOPHILITK. PROCHLORITE, I'LIXOC'HLOKK, AND PEXXTXTTE. 



The minerals of the chlorite group, according to Tschermak, may be 

 regarded as isomorphous mixtures of amesite (H 4 Mg 2 Al,Si0 9 ) and serpen- 

 tine (H 4 Mg 3 Si 2 9 ) molecules, although Clarke dissents from this conclusion. 

 Tschermak gives the range of the various orthochlorites as follows : 



Amesite: At to At 4 Sp. 



Corundophilite: At 4 Sp to At 7 Sp 3 . 



Prochlorite (ripidolite) : At ; Sp 3 to At 3 Sp 3 . 

 Clinochlore: AtsSp 3 to At Sp. 



Penninite: At Sp to At,Sp 3 . 



These would correspond to the following compositions: 



Amesite: 



H 4 Mg,Al 2 Si0 9 to H 20 Mg n Al s Si s O 45 . 



Monoclinic. 



Sp. gr. 2.71. 



Corundophilite: 



H 20 Mg n Al 8 Si 6 O 45 to H 40 Mg, 3 Ali 4 Si 13 O„ . 



Monoclinic. 



Sp. gr. 2.90. 



