J. H. Pratt — Miner alog iced Notes. 



215 



mentions zircon as one of the rock constituents. Some speci- 

 mens of these zircon crystals have been sent to this laboratory 

 recently by Prof. Adams for crystallograpkic investigation and 

 as they present several points of interest a brief description of 

 them is given here. 



The crystals occur imbedded in the usual manner in the 

 rock, from which they can readily be separated in a nearly 

 perfect condition. They show two quite different habits, one, 

 represented in tig. 5 in which by the development of two 

 opposite pairs of the pyramidal faces together with a pair of 

 the prisms of the second order, the crystal becomes columnar 



in this direction and mimics a hexagonal prism of the second 

 order terminated by rhombohedral faces. The only forms 

 observed on these are : 



a, i-i, (100) ; andjo, ], (111). 

 In the second habit the pyramidal faces are strongly devel- 

 oped, while the prism faces are short or lacking altogether. 

 These crystals represented by fig. 6, show the following forms. 

 a, i-i, (100); m, I, (110) ; v, 2, (221); p, 1, (111). 

 The crystals are well suited for measurement and give fair 

 reflections of the signal on the goniometer. In the following 

 table of calculated and measured angles, the elements of 

 Kupffer* were used to obtain the calculated angles, where, 

 Axis c'= 0-640373. 



rn^p, 



p *p', 



p Ai?" 



In conclusion the author desires to express his thanks to Mr. 

 L. V. Pirsson for valuable aid during the progress of the work. 



Laboratory of Mineralogy and Petrography, 

 Sheffield Scientific School, New Haven, June, "1894. 



* Dana's Mineralogy, sixth edition, p. 482. 





Calculated. 



Measured. 



110/slll 



47° 50' 



47° 42' 00" 



110/^221 



28 54 



28 52 



100/vl 11 



61 40 



61 38 



infill 



56 40 26" 



56 38 



nielli 



84 20 



84 16 



