.368 C. Palache — Powellite Crystals from Michigan. 



quality of its faces is sufficiently good to insure accurate 

 measurements. 



The measurements were made on a two circle goniometer 

 (Goldschmidt model) and the observed angles therefore appear 

 in the form of the angular coordinates, <£> and p, as used in the 

 Winkeltabelle of Goldschmidt. 



The forms observed were : 



p(lll) 6(101) 



A (133) 



j?(3'l 1-11) Je(l5t 



>) J(ni-ii). 



and the following 

 angles. 



table shows the observed and calculated 



Symbol. 



Observed angle. Calculate 



<p p $ 

 00° 00' 57°04f 00° 00' 

 44 59 65 24 45 00 

 18 28 58 25| 18 26 

 15 08 58 00 15 15 

 11 19 57 38 11 18 

 5 11 57 08 5 11 



d angle. 



Letter. Miller. Gold't. 

 e Oil 01 

 p 111 1 

 h 133 |1 

 j 3-11-11 T 3 T 1 

 h 155 \\ 

 I 1-11*11 JU 



p observed. 

 57° 00' 3 

 65 24 2 

 58 26 2 

 58 00 3 

 57 35 1 

 57 11 1 



As shown by the accompanying figure, the pyramidal hemi- 

 hedrism is strongly emphasized by the faces of h (133) and 

 ^'(S'll'll), the first especially being broad and of perfect 

 quality. The other two hemihedral forms, h (155) and 

 (l-ll'll) were very narrow faces in the zone, and as they were 

 each observed but once they must be 

 considered as doubtful and were there- 

 fore not introduced into the figure. 

 There is a tendency for these planes to 

 form a striated or curved surface between 

 the forms p and e such as Melville 

 observed, but there were two zones on 

 the crystal in which the faces were 

 sharply enough bounded to give good 

 measurements. 



The measurements lead to the same 

 axial ratio as those made by Melville and 

 the isomorphism of the species with the 

 scheelite group is thoroughly established. 

 With the crystals of powellite sent by Dr. Hubbard was 

 another specimen of the mineral of quite a different appear- 

 ance. It consists of a rounded mass of powellite about two 

 centimeters in diameter, upon which are a few small fragments 

 of rocky matrix, minute crystals of bright green epidote and 

 two or three shreds of native copper. On the broken surfaces 

 the powellite shows an imperfect cleavage, seemingly parallel 

 to 6(101). The central part of the specimen is of the same 



