Palache and Wood — Orystallograjohio Study of Millerite. 345 



The garnet is green in color, varying from a yellowish tone 



in massive specimens to a deep emerald-green in the sparkling 



transparent crystals. 



The following analysis by T. Sterry Hunt is taken from 



Dawson. Geologv of Canada, p. 497. 



I. II. 



Si0 2 .._ 36-65 



A1 2 3 17-50 



Cr 2 3 6'20 6-93 



FeO 4 97 4-80 



CaO 33-20 33-29 



MgO 0-81 



Volatile 0*30 



Total 99-63 



The analysis shows that the garnet is ouvarovite, but with a 

 very small proportion of chromium. 



Specks of chromite are embedded in the garnet, in places 

 quite abundantly. 



The pyroxene is yellow-gray or pale green, and is either in 

 isolated crystals embedded in calcite, in granular masses con- 

 sisting almost wholly of this mineral, or in minute crystals 

 implanted on the surface of garnet aggregates. The crystals 

 are prismatic and are often large, up to six or more inches in 

 length. The pinacoids «, (100) and h, (010) are dominant, and 

 narrow faces of the prisms m, (110) and i, (130) are always 

 present. These forms always have smooth and brilliant faces ; 

 the terminating planes, on the contrary, are always dull and 

 measurements could be obtained only with great difficulty. 

 The forms p, (101) and u, (111) are always present and occa- 

 sionally minute faces of c, (001), s, (111), and several other 

 pyramids not corresponding to established pyroxene forms 

 were noticed. Twins on the common pyroxene law, (100) the 

 twinning plane, are common. No analysis of this material 

 could be discovered. 



The calcite vein -filling is snow-white and very coarsely 

 granular, individual cleavage rhombs up to three inches across 

 being at hand. It is characterized by an_extreme develop- 

 ment of pressure-twinning parallel to <?, (0112), so that a part- 

 ing parallel to the negative rhombohedron with smooth reflect- 

 ing surfaces scarcely inferior to those of the cleavage, is often 

 obtained. The occurrence of this t winning-parting in the 

 calcite is especially noteworthy, since this identical structure 

 is also developed in the millerite, as will be shown presently. 



Millerite Occurs scattered through the massive garnet, more 

 abundantly at the boundary between garnet or pyroxene and 

 calcite, and finally wholly embedded in calcite. The aggre- 



