72 



NEW YORK STATE MUSEUM 



in the zone [ooi . no] and are, for the most part, brilliant and sharply 

 defined. Vicinal developments which were noted throughout this 

 zone are probably due to the rounding of the edges characteristic 

 of this variety. Twinning parallel to a is common to this occur- 

 rence, the twinning habit producing sharply defined reentrant 

 angles between c and c The forms observed with their measured 

 and calculated angles are given below: 



SUMMARY OF MEASURED AND CALCULATED ANGLES 



Form 





Angle 



Measured 



Calculated 











o / 



/ 



C 



OOI 











a 



no 











h 



OIO 











m 



no 



c:m 



OOI :iio 



6S i6 



65 30 







m,:m"' 



iioriio 



66 17 



66 29 







h:m. 



oio:iio 



56 46 



56 46 



n 



III 



c:n 



OOI :iii 



38 4 



38 16 







n:n' 



III :iii 



43 25 



43 49 



V 



221 



c:r} 



OOI :22I 



49 7 



49 15 







v:r} 



221 :22I 



54 25 



54 18 



t 



III 



c :i 



OOI :iii 



70 i7i 



70 23 







t:t' 



III :iii 



68 53 



69 9 



I 



112 



c'.i 



OOI :ii2 



40 25J 



40 34 



* Apatite 



Apatite occurs quite abundantly both as a primary mineral 

 associated with orthoclase and hornblende in large crystallizations, 

 and as a secondary mineral, deposited from resolution of the former 

 phase in small crystals associated with the calcite of types III, IV 

 and V. Both phases of apatite give distinct reactions for chlorine 

 and fluorine. The crystals of the first generation were obtained 

 from the vug opening into the 600-foot level which furnished the 

 large hornblende crystals previously described. Like these, the 

 crystals of apatite are in many instances of unusual size, the one 

 shown in plate 1 1 measuring 7 cm in diameter while many of those 

 lining the walls of the vug were considerably larger. They show 

 marked indications of an aqueo-igneous origin and were undoubted- 

 ly subjected to considerable mechanical stress when still in a plastic 

 condition. A striking evidence of this latter fact is given by the 

 specimen shown in plate 11. In this instance heart-shaped 



