S. L. Penfield—Phenacite from Colorado. 131 
In addition to the above, Des Cloizeaux identified a third 
prism &, 4150, 7-8, aud a new plane which he lettered z, 1344, —71-4 
which were not identified on the crystals which I have ex- 
amined. In lettering the forms I have followed Kokscharow, 
with only a few deviations, 7, z, wand m above equal &, 7, m 
and g respectively of other authors. 3 
All of the crystals which I have seen occurring on the feld- 
spar are lenticular in shape, resulting from the slight develop- 
ment of prismatic and predominance of rhombohedral forms. 
Fig. 1 represents the form of crystals which occur with topaz on 
a brownish, lamellar albite. This specimen is in Prof. Brush’s 
collection, labeled only Pike’s Peak: the crystals are a trifle 
simpler than those occurring on the amazon stone from Floris- 
sant, and it may he that they are from some other special 
locality in the Pike’s Peak region. Here the rhombohedron r 
predominates, d is large, and the two forms p and p, are, as is 
usually the case, about equally developed; the other forms z, 
a and m are at times wanting, and scarcely ever more developed 
than shown in the figure. The crystals occurring on the 
amazon stone are usually more highly modified. Fig. 2 repre- 
sents the forms which were observed on a crystal from Mr. C. 
S. Bement’s collection, while fig. 3 is a basal projection of the 
same with the position of the lower faces dotted in, which is 
well suited to show the tetartohedral character of the crystal. 
All of the forms mentioned in the above list are shown in these 
figures except # and m3; # was not observed on this crystal, 
and m only as a very narrow face. While the usual custom 
has been followed of drawing these crystals so that an edge of 
the positive rhombohedron above runs toward the observer, 
the basal projection has been so turned that the positive rhom- 
bohedron above is in front, so that the indices in the above list 
of forms can be better understood. The relative size and posi- 
tion of the rhombohedrons of the first order can readily be 
understood from the figures. Of rhombohedrons of the second 
order there is a decided predominance in size of p to the right 
