Van Horn and Hunt — Hournoniie Crystals. 149 



leaves little doubt as to the identity of the forms cited below. 

 When the crystal faces were quite small, and the surface con- 

 tact unreliable, small pieces of cover glass were cemented to 

 the surfaces in question, and reflections obtained in the usual 

 manner. 



Crystal No. 1. — Crystal No. 1 (Holden Collection) was the 

 largest of the three specimens examined, and is shown in fig. 2. 

 Unfortunately it had been broken in two, and before com- 

 plete measurements could be obtained, the fractured surfaces 

 were glued together, and finally supported by plaster of paris, 

 (the full and long dashed line on the faces <?(101), and a(100) 

 represents the glued contact, while the unshaded space be- 

 tween the short dashes represents the plaster cast). The 

 specimen thus reconstructed was short prismatic in develop- 

 ment, and revealed the following 9 crystal forms : the pina- 

 coids, a(lOO), 6(010), c(001); the prisms, m(110), *'(130),/(120); 

 the domes, o(101), n(011); and the pyramid w(112.) The 

 angular measurements obtained, as well as the corresponding 

 theoretical values are given in the following table : 







Contact Measurements 



Calculated Angles 



m:m = (110) 



(lio) 



8*7° 



30' 



86° 



20' 



/•-/ = (120) 



: (120) 



56 





56 



8 



i:a = (130) 



: (100) 



71 





70 



26 



o:a — (101) 



(100) 



47 





46 



17 



c:u =z (001) 



(112) 



32 





33 



15 



c:n = (001) 



: (011) 



43 





41 



54 



n: m = (011) 



: (110) 



63 





62 



49 



Crystal No. 2 — Crystal No. 2 (Case Collection) illustrates 

 a prismatic type of development in the direction of the brachy 

 axis (a). A drawing of this crystal is shown in fig. 3. 

 The right-hand side of this crystal was more or less broken off, 

 and a photograph of the opposite, or more perfect side, is 

 shown in fig 1, with the basal pinacoid, c(001) at the top, and 

 the macropinacoid, #(100) on the right. This specimen had 

 been glued together at some time previous to its arrival for 

 crystallographic orientation (the full and long dashed line on 

 the faces c(001), A(203), i?(223), and a(100) represents the 

 glued contact). This specimen was found to contain 12 forms 

 which was more than were observed on either of the other 

 crystals as follows: — the pinacoids, a(100), 5(010), e(OOL); the 

 prisms, m(110), t?(310), 3>(140), a(230); the domes, 2(201), 

 A(203), 7(023) ; and the pyramids, i?(223), and £(211). The 

 forms were identified, and their relationship established on 

 the basis of the following measurements : 



