CONTRIBUTIONS FROM THE HARVARD MINER ALOGICAL 



MUSEUM — XIV. 



CRYSTALLOGRAPHIC NOTES ON MINERALS FROM 



CHESTER, MASS. 



By Charles Palache and H- O. Wood. 



Presented March 9, 1909. Received March 1G, 1909. 



The minerals of Chester, Mass., have long been the subject of inves- 

 tigations by many mineralogists, especially from the chemical and 

 genetic standpoints. All such studies are cited, and their substance, 

 together with very much more that is original, is fully presented in 

 Emerson's well-known works. 1 The following notes, chiefly crystal- 

 lographic, are presented because this aspect of the Chester minerals 

 has been almost wholly overlooked in what has been hitherto published. 

 The material studied was collected by the authors during the years 

 1902, '03, and '04, at the end of the last working period of the emery 

 mine. The observations on diaspore were made by Mr. Wood ; the 

 remainder of those presented in the paper, by the senior author. 



Diaspore. Diaspore crystals from Chester were first described by 

 Dana, 2 whose brief paper remains the sole crystallographic study of 

 any Chester mineral. Since his description appeared the mineral has 

 been found in several new phases which seem to deserve added record. 



Diaspore occurs in three fairly distinct habits : 



Type a, long and slender, acicular or bladed crystals. 



Type b, flat, disc-like crystals, tabular parallel to the brachypinacoid, 

 with narrow prism and pyramid faces and larger, curved brachydomes. 



Type c, short, stout crystals having prisms and pyramids about equally 

 developed, sometimes quite without the brachypinacoid, and then pris- 

 matic parallel to the a axis. 



1 B. K. Emerson, A Mineralogical Lexicon of Franklin, Hampshire, and 

 Hampden Counties, Mass., Bull. U. S. G. S., 126, 1895. The Geology of Old 

 Hampshire County, Mass., Monograph U. S. G. S., 29, 1898. 



2 Dana, E. S., Mineralogical Notes : Diaspore from Chester, Mass., Am. 

 J. Sci., 32, 388 (1886). 



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