ANALYSES AND OPTICAL PROPERTIES OF AMESITE AND 

 CORUNDOPHILITE FROM CHESTER, MASSACHUSETTS, 

 AND OF CHROMIUM-BEARING CHLORITES FROM CALI- 

 FORNIA AND WYOMING. 



By Earl V. Shannon, 



Assistant Curator, Department of Geology, United States National Museum. 



INTRODUCTION. 



The present paper records work done in the laboratory of the 

 department of geology upon several chloritic mmerals as part of 

 a general, though interrupted, study of the complicated and im- 

 perfectly understood a*gregation of substances commonly referred 

 to collectively as the chlorite group. Previous work done by the 

 present writer upon materials of this class has already been pub- 

 lished, including analyses and optical properties of diabantite 

 stilpnomelane and chalcodite from Wcstfield, Massachusetts,^ stil- 

 pnomelane from Lambertville, New Jersey,- and prochlorite from 

 Trumbull, Connecticut, and Washington, District of Columbia.^ 

 These investigations have not, as yet, furnished evidence upon 

 which to base any new theoretical views as to the chemical nature 

 of the various members of the group and discussion of the constitu- 

 tion either of the individual minerals or of the group as a whole is 

 deferred until additional work shall have explained many points 

 which are not now clear regarding variation in chemical composition 

 and optical properties of the several constituents of the group. 

 The work upon these minerals will be contiimed as good materials 

 come to hand, or as the need for reinvestigating individual species 

 becomes apparent. 



AMESITE FROM CHESTER, MASSACHUSETTS. 



The name amesite was given by C. U. Shepard to a pale green 

 chlorite occurring in intimate association with diaspore at the old 

 emery mine in Chester, Massachusetts. The mineral which was 

 analyzed by Pisani * is described as in hexagonal plates; foliated, 



» Proc. U. S. Nat. Mus., vol. 57, 1920, pp. 397-403. 



2 Idem (in press). 



3 Idem (in press). 



< Pisani, Compt. Rendus Acad. Sci., vol. S3, 187C, p. 166. 



Proceedings U. S. National Museum. Vol. 58— No. 2342. 



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