DIABANTITE, STILPNOMELANE, AND CHALCODITE OF 

 THE TRAP QUARRIES OF WESTFIELD, MASSACHUSETTS. 



Bj Earl V. Shannon, 



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



Throughout the Triassic area of the Connecticut Valley the diabasic 

 sills, dikes, and flows are decomposed to a greater or less extent, 

 the most universally common product of this alteration being an 

 earthy deep-green chlorite. Similar chlorites occurring as coloring 

 matter in altered diabases of Frankenwald and Voigtland were 

 early analyzed by Liebe and named diabantachronnyn. In 1875 

 Hawes^ analyzed such a chlorite from the amygdaloid trap of the 

 Farmington Hills, Connecticut, deducing a rational formula from 

 four careful analyses made upon pure homogeneous material. Hawes 

 shortened Liebe's ponderous name to diabantite. So far as known 

 to the writer no chemical work on this mineral has since been pub- 

 lished. Emerson in his descriptii3n of the Deerfield Dike,^ in his 

 Monograph on the Geology of Old Hampshire County,' and in the 

 accompanying Mineralogical Lexicon,* mentions many and varied 

 occurrences of green chlorite which he referred to diabantite, but he 

 apparently made no chemical analyses. In fact, in the Deerfield 

 paper he remarks as follows: "That the mineral is chemicall}^ iden- 

 tical With, that analyzed by Hawes and named diabantite by him is 

 extremely probable in view of their identity in all chemical and 

 especially optical properties, and of the monotonous similarity of the 

 many diabase dikes of the Connecticut basin in which both occur. 

 That the mineral is distinct from delessite, as the word is used by 

 Zirkel, Rosenbusch, and Heddle, is much less certain." 



During the past year the writer has frequently visited the quarries 

 of the Lane company, in the outcrop of the Holyoke Trap sheet along 

 the west line of the town of Westfield, Massachusetts. These quar- 

 ries are well known to mineralogists for the many superb specimens 

 of datolite which they have produced. The location of the quarries 

 and the general mode of occurrence of the minerals have been noted 

 in a brief paper published by the present wi'iter after a first visit.^ 



1 Amer. Joum. Sci., vol. 9, 1875, p. 454. « U. S. Geol. Survey Bull. 126. 



s Idem, vol. 24, 1882, pp. 198-201. s Amer. Mineral., vol. 4, 1919, No. 1 p 5 



' U. S. Geol. Survey, Mon. XXIX. 



Proceedings U. S. National Museum, Vol. 57— No. 2316. 



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