372 S. L. Penfield — Spangolite, a new copper mineral. 



tallographic and chemical investigation. A number of small 

 crystals were selected which were measured in the prominent 

 pyramidal zones between the basal planes. The basal planes 

 usually gave very good reflections of the signal but on turning 

 the crystal on the goniometer, after the pyramids came into a 

 position to reflect light, there usually followed an unbroken 

 band of signals reflected from these faces owing to their stria- 

 tions and oscillatory combinations. In this band of reflections 

 prominent parts could usually be located which indicated the 

 position of distinct pyramidal faces. On measuring fifteen 

 independent pyramidal zones on five different crystals, only 

 one crystal was found, which we will designate as No. 1, that 

 gave sharp reflections from the pyramidal faces ; from this an 

 angle was obtained of c*p, 0001^2112 = 63° 32'. Still better 

 results were obtained on measuring from pyramid to pyramid 

 when the reflections of the signal are not so much disturbed 

 by the striations and the value given below, which will be 

 accepted as the fundamental measurement, was obtained 



p *p', 2112 a 1122=53 c 11' 30" 



from which we calculate the length of the vertical axis 

 c=2-0108. 



The largest of all the crystals, which we will designate as 

 No. 2, was fortunately so situated that it could be measured 

 without detaching it from the specimen. It was very sym- 

 metrical and had the habit shown in fig. 1 ; it measured about 

 gmm j n di am eter and was 5-| mm high. Five out of the six pyr- 

 amidal faces p at one end of the crystal were quite perfect, 

 being only slightly distorted by the horizontal striations. Some 

 of the faces were so situated that reflections could not be 

 obtained from them without detaching the crystal, but a num- 

 ber of very satisfactory measurements were made which are 

 given below. The accompanying table contains a summary of 

 the measurements which were made on the two best crystals 

 from the faces c, 0001, O ; p, 2112, 1-2 ; o, 2114, J-2 and in, 

 1010, 1 ; all of which gave sharp reflections of the signal. The 

 measurements were made on a Fuess goniometer, using the 

 signal and the ocular ft of Websky. The one marked with an 

 asterisk was taken as fundamental. 











Table 



I. 





♦ 











Crystal No. 



1. 





Crystal No. 2. 



Calculated. 



p A p', 



2112 



a 



1122 



53° 11' 



30 



'* 



53° 13' 45" 



53° 11' 30" 



p' A p", 



1122 



^ 



x212 









53° 11' 45" 



u 



p" A p'" 



1212 



A 



2112 









53° 14' 



u 



p A p iv , 



21.2 



A 



.122 









101° 43' 



101° 41' 



P - o v , 



2112 



A 



1214 



50° 48' 







50° 51' 



50° 51' 



P ~ c, 



2x_2 



A 



0001 



63° 32' 









63° 33' 30" 



p aw, 



2112 



A 



1010 



39° 4' 









' 39° 9' 



