A CRYSTALLOGRAPHIC STUDY OF THE DATOLITE FROM 

 WESTFIELD, MASSACHUSETTS. 



By Earl V. Shannon, 



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



INTRODUCTION. 



The locality of Westfield, Massachusetts, has within the past 18 

 years produced datolite crystals in such abundance and of such 

 unusual size and perfection of form that the specimens have become 

 well known and are now widely distributed in mineralogical collec- 

 tions. The datolite of this occurrence was first described by Whit- 

 lock, 1 whose work apparently was based on only a few crystals. 

 Upon these 27 forms were found, four of which were new. Imme- 

 diately following the publication of Whitlock's paper, Kraus and 

 Cook 2 published a more extensive study of this datolite, their col- 

 lection consisting of some 45 crystals, of which 10 were measured 

 in detail. They added three new forms to the list and found a 

 number of previously known forms not present on the crystals 

 examined by Whitlock. Later Gorgey and Goldschmidt, 3 in a gen- 

 eral study of datolite, examined 11 crystals from Westfield, upon 

 which they found eight new forms ; and later still Ungemach 4 has 

 reviewed all previous work on the mineral from this locality and 

 measured eight crystals on which nine additional new forms were 

 found. Thus 23 new forms had been found in the study of only 

 approximately 70 crystals from a locality which had produced 

 thousands of crystals of datolite — a fairly dependable indication that 

 additional studies based upon the mineral from this locality might 

 produce interesting results. 



While a resident at Springfield, Massachusetts, between February, 

 1918, and April, 1919, the present writer had opportunity at frequent 

 intervals to visit the quarries which yield the datolite. The modes 

 of occurrence of the datolite and associated minerals were carefully 

 observed with a view of describing the locality, and the crystallo- 



i Bull. 98, N. Y. State Mus., pp. 19-22, 1905. 



1 Amer. Journ. Scl., vol. 22, p. 21, 1900. 



» Zeitschr. Kryst., vol. 48, p. 652, 1910. 



« Ungemach. Zeitschr. Kryst., vol. 49, p. 470, 1911. 



Proceedings U. S. National Museum. Vol. 59-No. 2385. 



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