280 A. J. Moses — Crystallization of Luzonite. 



The Calculated Angles of Enargite. — The axial elements 

 calculated by Dauber* in 1854 are 



d:b\ c = 0-8711 : 1 : 0-8218 



based upon angles of mm = 82° T and cs = 39° 3P. 

 In 1895 Fletcherf calculated new elements 



d:h: c = 0-8691 : 1 : 0-8308 



based upon angles mm = 82° 0J' and ck = 43° 12' 



This value of mm is the average of so many measurements 

 that it cannot well be questioned and it is not far from the 

 angles here obtained since the mean of twenty (/> angles of 110 

 and 223 is 48° 57-J' and Fletcher's mm = 82° 0*' yields <£ of 

 110 = 48° 59f ! . 



Fletcher's value for c, however, considers only the faces 

 k = 101 and is the mean of some fourteen values of ck. The 

 new pyramid, P = 223, is represented on crystals JS T os. 3 and 4 

 by eight good faces and the readings especially in crystal 4 are 

 close. The angles <j> and p of 223 in crystal 4 yield a : b : e — 

 •8698 : 1 : -8241, essentially those of Fletcher in the case of a 

 but not so near in the case of c. 



I have therefore used in my calculation an intermediate 

 value for c of -8274, which is also an approximate mean be- 

 tween the c values of Fletcher and Dauber. 



In conclusion, these results show that the crystals which form 

 at the solidification of luzonite and those which form possibly 

 later on luzonite have the angles of enargite. In other words, 

 " luzonite " is not an independent species but merely a variety 

 of enargite. 



I base this claim principally on the angles here recorded for 

 the small and relatively simple crystals Nos. 1 and 2, which are 

 types of the cavity-wall crystals so connected with the massive 

 material that it is impossible to doubt that they are the results 

 of its solidification. 



Crystal No. 3 I believe to have formed in the same 

 manner but under more favorable conditions, while crystal No. 

 4 is evidently secondary. The new form P = 223, prominent 

 in both, connects them however. 



The observed color difference on the terminal faces and ver- 

 tical faces of the cavity-wall crystals, and crystal No. 3, prob- 

 ably has genetic significance. The recorded analysis by 

 Winkler is of practically pure material, which makes inadmis- 

 sible a theory of crystallographic regularity in elimination of 

 impurities. The comparative dullness of the basal plane in 

 Nos. 1 and 2 might suggest a light effect explaining the color, 



*Pogg. Ann., lxxiii, 383, 1854. 



f Mineralogical Magazine, xi, 73, 1895. 



