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 i8J', and g A c (cleavage) = 19 18', the calculated value for 

 these angles being 32 23^' 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 jthe clino_ dome g (012) and three prominent hemipyra- 

 mids e (112), A (ii3)_and /u, (114) in the zonefooi.no]. These 

 gave the indexes 148, 149 and 1.4.10 respectively and were assigned 

 the letters e', A/ and //,' '. 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 ,(ioo) ; b, (oio) and c (ooi) 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 % (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 O (018), the 

 latter sometimes present. 



1 In measuring the dull faces, notably 012 and 018 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. 



