Palache — Notes on Tellurides from Colorado. 



421 



rich in forms as shown in fig. 2 and is sometimes deeply 

 striated. It forms a satisfactory means of distinguishing the 

 positive from the negative octants, which in its absence, owing 

 to the nearness of the angle j3 to 90° in sylvanite, is not always 

 easy to do. 



Of the other pyramidal forms, cr, 121, is the most common, 

 being rarely absent and generally relatively large in size. The 

 other pyramids, both positive and negative, and the prisms are 



of very subordinate importance in defining the outlines of the 



crystals. 



| fcTwo of the measured crystals were found to be twinned 



according to the common law for sylvanite, twinning plane the 



orthodome, L01. Figs. 3 and 4 reproduce these twinned crys- 

 tals in about the proportions of the originals. Fig. 3 will be 

 seen to be a simple contact twin, in which, however, the two 



