S. L. Penfield—Phenacite from Colorado. 133 
hedron of the third order s. Atthe top of the crystal are 
the three small faces of the minus rhombohedron d. The 
prismatic faces are striated not only vertically, especially that 
part of the prism farthest away from the s face, but also near 
each s face parallel to the intersection between s anda. ‘These 
two sets of striations do not cross but meet along a line run- 
ning in an inclined direction across the a face; the s and r faces, 
especially the former, are also striated parallel to the intersec- 
tion between s anda. ‘These striations point to vicinal faces, 
prisms and rhombohedrons of the third order, but no definite 
indices could be assigned to them. The 2 faces are not smooth 
and polished, but covered with little prominences with curved 
unsymmetrical contours. Crystals with exactly this habit have 
previously been described by Prof. M. Websky,* of Berlin, 
from.an unknown locality in Switzerland, and they are the only 
crystals, so. far described, which are terminated mainly by 
rhombohedrons of the third order. It is interesting also to 
note that, while in the Russian localities the crystals of phena- 
cite occurring on amazon stone are lenticular, as is the case 
also in Colorado, the crystals from the emerald mines of 
Katharinenburg are prismatic, terminated however not by 
rhombohedrons of the third, but by those of the first and 
second order. 
In the following table the angles are given which were 
measured for the identification of the above mentioned forms 
and also the corresponding angles calculated from the funda- 
mental angle of Kokscharow, + .7’, 1011 .1101=63° 24’, c==0-66106. 
In measuring those faces which are deeply striated, and where 
there were a number of reflections of the signal the most promi- 
nent reflection was chosen. 
* Jahrb. f, Min., 1882, i, 207. 
