1883.] Crystallography of Miargyrite. 373 



Millerian elements— am 41° 23' 79, bt 27° 24'4, c??i 39° 58'79 ;— 

 have been calculated. These are equivalent to 



a : b : c = 30017 : 1 : 2-9166 ; v = 81° 22''58. 

 The forms observed on the several crystals were the following: 



Crystal 1. Fig. 2. 



a, rj, d, s, t, b, m, (105), c, M, o, R, yjr, £, A-, A;. 



This is a remarkably good crystal ; £ and k are fairly well de- 

 veloped, the former gives good images, the latter poor ones: yjr and 

 h are very minute, and reflexions are obtained in the zone [a£] 

 between £ and yjr, giving angles £ © 3° 22' or 4° 15' or 4° 56'. 



Crystal 2. Fig. 4. 

 a, ?7, f, <$>, d, s, t, <w, c, o, iV, ^, yfr, g, £, h, w (12 1 15). 



A good crystal on which £ is the most prominent plane on one 

 side. A plane (12 1 15) is well developed on this crystal. The 

 plane g is badly developed, and gives several images, so that ag 

 may be 59° 50', 60° 8', 60° 18', 61° 15'. The planes q on opposite 

 sides of N are not in a zone with N as was determined by measur- 

 ing qq t = 31° 51'i (poor). There is also a badly developed plane 

 giving an indefinite reflexion lying between q and yfr, so that 

 aA=40°53' nearly. This plane may therefore be (1126). For 

 (11 26) we have («,TI 26) = 40° 51' 33. 



Crystal 3. a, d, s, t, w, (105), c, o, g, jd, or (717). 



There is a rough pitted plane in the zone [adst] on this crystal 

 which may also possibly be in a zone [0#]. In this case it would 

 be (111). 



In the zone [ew^sj ^ s ^ ie pl ane ^ (1? 66) already mentioned. 

 Crystal 4. Fig. 8. 

 a, f, d, s, t, x, a, i, L, m, X, c, M, o, p, y, ir, g, h, ft, z, (16 16) ? 

 The planes are all small, and the crystal top has a rounded 

 aspect from the number of small faces. The planes in the 

 zone [og] are all much rounded and hardly allow of exact deter- 

 mination. On one side images extend in an almost continuous 

 band through an interval of 17° with brighter portions at intervals 

 of about one or two degrees. 



Another crystal of much the same development was considerably 

 distorted, and gave very poor measurements. It showed the planes 

 R, k, <w in addition to those on the former. The zone [R^'J was 

 measured. 



rat t = 39° 36' 

 tR 63° 46' 

 (64° 25') 



