The Monoclinic Pyroxenes of New York State. 



139 



Locality c/\t 2 Vna 



Diopside, Nordmarken 38° 3^ 58° 52^ 



White pyroxene, Kussinsk, Ural 38° 34^ 58° 45' 



Diopside, Schwarzenstein, Tyrol 39° 4^ 58° 56' 



Green coccolite, Arendal 40° 22' 58° 38' 



Schefferite, Langban 44° 25|' 65° 3' 



Diopside, Nordmarken 44° 42' 60° 28' 



" " 45° 21' 66° 44' 



Hedenbergite, Tunaberg 47° 10' 59° 52' 



Augite, Frascati 54° 68° 



Method of Cutting Sections at Right Angles to the Acute 



Bisectrix. 



In cutting sections of the crys- 

 tals for the purpose of measuring 

 the axial angle some difficulty was 

 at first experienced in getting the 

 section cut at just the desired 

 angle, as no saw for sectioning 

 brittle minerals in any desired 

 direction was at hand. The fol- 

 lowing method was devised and 

 on account of its simplicity and 

 the uniformlj^ good results ob- 

 tained seems worthy of mention. 



A frame of hard polished steel 

 was made of the shape, shown in 

 the upper part of Fig 1. On the 

 clinopinacoidal face, or a ground 

 -plane corresponding to it, there is 

 scratched a line representing the 

 trace of a plane normal to the 

 acute bisectrix. The crystal is then fastened in the frame with 

 a piece of wax so that the line coincides with the upper surface 

 of the frame, and plaster of paris poured in around it and allowed 

 to harden. The crystal is thus firmly embedded in the frame as 

 shown in the lower cut of the figure, and is ground down until 

 its surface is even with that of the steel frame. The crystal is 

 then removed, the ground surface polished and cemented to a 

 glass slip and the other end of the crystal ground down in the 

 usual way. 



