Kraus and Cook — Datolite from Westfield, Mass. 21 



Art. VI. — Datolite from Westfield, Massachusetts ; by E. H. 

 Kraus and C. W. Cook. 



Several months since, the Mineralogical Laboratory of the 

 University of Michigan purchased from Ward's Natural 

 Science Establishment of Rochester, _N. Y., an excellent suite 

 of datolite crystals from Westfield, Mass. At that time, 

 crystals of datolite from this locality had not been described, 

 and it was therefore decided to carry out a chemical and 

 crystallographical investigation of the same. Recently, how- 

 ever, Whitlock"* described several datolites from this locality. 

 Whitlock confined himself to a crystallographic study of these 

 interesting crystals, and since our investigations not only cor- 

 roborate many of his observations, but also give some additional 

 facts, we have thought it wise to present the same in detail. 



Crystallography. — The original purchase consisted of six- 

 teen crystals varying from an half to an inch and an half in 

 diameter. Subsequently fifteen others were added, so that 

 thirty-one crystals from this locality are now in the possession 

 of this laboratory. However, through the kindness of Ward's 

 Natural Science Establishment, all of the material in their 

 possession was placed at our disposal, so that, in all, forty-seven 

 crystals were examined. 



According to Mr. R. F. Jones, by whom the crystals were 

 collected, the datolite occurs in the cracks and crevices of Lane's 

 Trap Quarry, Westfield, Mass., half way between Springfield 

 and Westfield. f Most of the specimens seem to have been col- 

 lected during the past two years. AH the crystals are exceed- 

 ingly clear and transparent and of such sizes as to make 

 accurate goniometric observations possible. Four distinct types 

 of development were noted. 



Even though datolite has from time to time been studied 

 crystallographically, there is still considerable difference of 

 opinion as to the selection of the a and c axes. Although 

 Hess:}; and Schroeder§ had previously shown that datolite crys- 

 tallizes in the monoclinic system instead of orthorhombic as 

 assumed by Levy,|| Hauy,T" and Miller,** it remained for 

 Dauberft to positively establish the fact. The elements of 

 crystallization obtained by Dauber are : 



a:b: c=l-26574 : 1 : 0-63446 (3=90° 9'. 

 In so doing the form m x (fig. 1) was assumed as the unit 



*N. Y. State Museum, Bull. 98, 19. 



f Compare Whitlock, N. Y. State Museum, Bull. 98, 19. 



tPogg. Annalen, xciii, 380, 1854. 



§Ihid., xciv, 235, 1855 ; also xcviii, 34, 1856. 



|| Description d'une collection de mineraux, etc., pp. 179 and 182, 1838. 



^[Dana, System of Mineralogy, 6th ed.. 1892, 505. 



** Mineralogy, 1852, 408. 



ffPogg. Annalen, ciii, 116, 1858. 



