20 NEW YORK STATE MUSEUM 



are almost universally sharp and brilliant and fall well within 

 several clearly marked zones, greatly facilitating the ease and 

 accuracy of their identification. 1 



Cleavage was noted parallel to a, quite perfect, and parallel to 

 c, somewhat less so ; the measured angles gave m a a (cleavage) = 

 32 18^', and g a c (cleavage) = 19 18', the calculated value for 

 these angles being 32 2 3 J' and 19 22' respectively. 



Figures 37 and 38 represent the prevailing crystal habit, the 

 disposition of the planes in zones being shown in the spherical pro- 

 jection, figure 36. The intersection of zones in the plus half of 

 the projection is specially interesting. Three new hemipyramids 

 were observed in zone [001.140] as narrow faces beveling the edges 

 between the clino dome g (012) and three prominent hemipyra- 

 mids e (112), X (113) and p. (114) in the zone [001. no]. These 

 gave the indexes 148, 149 and 1.4. 10 respectively and were assigned 

 the letters e', X' and fj/. A plane in the zone [001.120] which is 

 quite prominent in these crystals gave the indexes 122 and is noted 

 in the text and projections as M. An enlarged projection of a 

 portion of one* of the typical crystals drawn in reversed position 

 to show the disposition of these rare planes is given in figure 39. 



Pinacoids. The three pinacoids a ,(100) ; b, (010) and c (001) are 

 commonly present, the two former as brilliant faces and the latter 

 as a somewhat dull series. The clinopinacoid b which is present 

 as a very narrow face serves as an excellent plane of reference in 

 orienting the crystal. 



Prisms. The faces in the prismatic zone are characterized by 

 considerable brilliancy. The prisms m (no) and o (120) are 

 commonly present; r (230) was noted in two instances on quite 

 small crystals. 



Domes. In the zone of the hemiorthodomes x (102) is promi- 

 nent giving to the combination a habit very similar to the Bergen 

 Hill and West Paterson occurrences; v (103) is often absent. The 

 presence of one or more hemidomes between a and x was noted in 

 several instances, but the faces were so minute and ill defined that 

 it was impossible to obtain any definite measurements from them. ■ 



The zone of the clinodomes is, on the other hand, very well 

 developed, showing m (on), g (012), t (013) and Q (018), the 

 latter sometimes present. 



1 In measuring the dull faces, notably pi 2 and 01S in the zone of the clinodomes and 103 in 

 the zone of the orthodomes, the method of placing a drop of alcohol on the dull face was success- 

 fully used to obtain a clear reflection of the goniometer signal. The face was brought into 

 approximate position and moistened by a drop of alcohol applied by means of a dropping tube. 

 The curved surface of the drop at first gives the effect of a series of multiple images; these, 

 however, as the drop reduces in thickness by evaporation, gradually merge to a center and at 

 the instant preceding complete evaporation combine in a clear and bright image of the signal. 

 The writer finds this expedient more satisfactory than the usual method of a cemented cover 

 glass and suggests it for crystals not soluble in alcohol. 



