Z. V. Pirsson — Remarkably developed Calcite Crystals. 63 



While the planes of the plus forms were generally smooth 

 and gave fair reflections of the signal, the minus forms were 

 always striated, resulting from an oscillation of them with the 



These striations were not however, as is often 

 blending the signals into an unbroken 



lines 



main face — f 1 ". 

 the case, mere 



band of light, but were distinct facets, often of some size. 

 As a result, each form gave a distinct reflection of the signal, 

 by which it was possible to recognize and measure it with a 

 fair degree of accuracy. The form — f 3 occurred as a distinct 

 pair of faces at the top of the striations and by covering the 

 latter with wax, the former could easily be measured with ex- 

 actness. The striations of these minus forms were also all in 

 one zone and this when determined aided greatly in their iden- 

 tification. Along the zone, the signal of each face stood out 

 sharply in a dim band of light connecting them and pretty 

 exact measurements could be made. The forms — 2 2 and — 4| 

 occurred most largely at the bottom and they are so represented 

 in ideal symmetry in the figure. At the re-entrant angle, 



7. 



the main plus form v, J 3 , and the main minus form ^J 3 , occur- 

 ring in about equal development, the crystal presents at this 

 end the appearance of the di- hexagonal pyramid. 



The following table of measured and calculated angles is 

 appended to show the identification of the forms. 



Angles of Scalenohedrons. 





Long edge. 



Short edge. 



Middle edge. 



I 3 (2131) 



calc. 



35° 35£' 



calc. 



75° 



22*' 



calc. 



132° 



58' 





meas. 



35 49 



meas. 



75 



24 



meas. 



133 



05 







36 10 





75 



07 





133 



07 



l 2 (3142) 



calc. 



24 10 









calc. 



113 



45 





meas. 



24 13 









meas. 



113 



26 



11 















113 



56 



P (7 4 11 15) 



calc. 



22 01 



calc. 



39 



41 











meas. 



22 04 



22 30 



meas. 



40 



40 









2 3 (2461) 



calc. 



37 30 















3 



meas. 



37 00 















-1 (4 8 12 5) 



calc. 



34 20^ 



calc. 



72 



22 











meas. 



34 20 ' 

 34 10 



meas. 



72 



23 









i 



calc. 



30 11£ 



calc. 



81 



16i 



calc. 



131 



30 



-f 3 (8 20 28 9) 



meas. 



30 01 



meas. 



81 



02 



meas. 



131 



29 







30 15 





81 



12 





131 



56 







30 11 



















30 18 















— 4§ (4 16 20 3) 



calc. 



meas. 



21 29^ 

 21 40 















And also the following angles : 



