Kraus and Cook — Datolitefrom Westfield, Mass. 27 



Natural etching is quite common, especially on the pyramids 

 Xjll3(, /xjlMJ and /ejll5| as noted by Whitlock.* This 

 phenomenon is also frequently observed on the prism e>{120[ 

 and the pyramid /3 { 121 } . In no case, however, were the figures 

 of sufficient size to permit an accurate determination of their 

 outline. 



Chemical Analysis. — For the chemical analysis one of 

 the clearest crystals weighing about ten grams was selected. 

 It was perfectly transparent and free from all inclusions. 

 Concerning the methods which were employed, it should be 

 stated that the boron trioxide was determined by the Goochf 

 method. Water was estimated as loss on ignition. The other 

 determinations were made according to the methods recom- 

 mended by Hillebrand.J Two analysis were made, which show 

 very close agreement. 

 The results are : 



I II Average 



Si0 2 37'60^ 37-58$ 37"59$ 



Fe 2 3 -10 -10 -10 



A1 2 3 __ _ -14 -16 -15 



CaO 34-64 34-74 34'69 



MgO .. -32 -31 -315 



B 2 3 21-76 21.94 2185 



H 2 _.. 5-67 5*76 5-715 



Total 100-23$ 100*59$ 100-41$ 



The average of the above analyses agrees very closely with 

 that required for the accepted formula HCaBSiO.. This was to 

 be expected because of the unusual clearness and purity of the 

 crystals. It is also to be noted that this analysis is very similar 

 to Bodewig's§ of the datolite from Bergen Hill, ~N. J., as is 

 shown by the following comparison : 



Theoretical Westfield Bergen Hill 



Si0 2 ...37-63 37-59 37'48 



Fe 2 3 -10 -12 



A1 2 3 -15 



CaO 34-95 34-69 35'42 



MgO -31 



B 2 3 21-81 21-85 21-14 



H 2 0__. 5-61 572 5-71 



Total 100-00 100-41 99-87 



*N. Y. State Museum, Bull. 98, 12. 



fF. A. Gooch, Am. Chem. Jour., ix, 23, 1887. F. A. Gooch and L. C. 

 Jones, this Journal, vii, 34, 1899. 



% Bulletins 148 and 176 U. S. Geol. Survey. 



§C. Bodewig, Zeitschr. fur Krys., viii, 211, 1884. 



