102 Moses — Mineralogical Notes. 



On account of the minuteness of the modifying faces the 

 measurements were made upon a Goldschmidt two-circle 

 goniometer, and it will be noticed that the angles obtained 

 deviate considerably from the calculated angles- The readings, 

 however, agreed well with each other and the variation from 

 the calculated angles are due principally to the fact that in 

 orienting the crystals, in the absence of the basal plane, the 

 prismatic zone was employed and in all recorded measurements 

 either of Chilian crystals'* or of those from Wallaroo, South 

 Australia, f there have been marked variations in this zone, so 

 great, even with the most perfect crystals, that the calculated 

 angles only result as an average of many different crystals and 

 measurements. 



It may be noted that many of the crystals are interpene- 

 trated and with some appearance of regularity. A careful 

 measurement failed to prove any true twinning. 



In the tabulation which follows I have calculated cj> and p 

 to the elements obtained by Smith,J viz: a : ~b\ c— 0*66130 : 

 1 : 0*75293, and have used as a meridian a position mid- 

 way between the reading for 110 and 110, assuming this to 

 be the true position of 010. Two new prisms were found, 

 (150) designated by 7, which occurred with s (120) on one 

 crystal in easily visible faces, the other (210) designated by (3 

 and of which two very narrow faces were observed which 

 yielded distorted reflections. All of the measurements with 

 the exception of 7 (150) were obtained from one bright little 

 crystal, almost octahedral in shape and approximately lf mm 

 parallel to d, ~b or b. Two other larger crystals were measured 

 and showed the same forms, but being less bright gave poorer 

 reflections. On one of these the (150) prism was found. 



The observed and calculated coordinates were : 





Observed. 



Face. 



<P P 



b 010 



0°08' 90 c 



y 150 



16 35 90 



s 120 



37 12 90 



m 110 



56 26 90 



£210 



72 05 90 



Calculated. 







P 



0° 



90° 



16 50' 



90 



37 05 



90 



56 31 



90 



71 42 



90 







36 59 



37 05 



62 06 



56 31 



53 46 



e 011 02 37 4' 



n 121 37 04 61 58 



r 111 56 21 53 39 



*See previous references. 



f Zepharovich, Ber. Ak. Wien, lxiii, 6, 1871; Klein, Neues Jahrb. f. Min., 



1869, 347; E. S. Dana, Mm. Mitth., ii, 103, 1874. {L. c. 



