242 WRIGHT— CRYSTALLOGRAPHIC PROPERTIES. [June 1, 
sionally hollow and resemble then Fig. 3 (crystal No. 8, 1.1 X 1.0 
<o0.4mm.). The central part of the prism faces is not filled out 
as yet, while the basal plane is perfectly flat. although in some cases 
a mere fragile paper-like film. The pyramid faces are usually 
present in the form of narrow strips. The hollow parts of the 
crystals seem to consist of a pile of innumerable thin plates piled 
one on top of the other, similar to the structure of a biotite crys- 
tal. The first type passes gradually into a thicker tabular one, in 
which the pyramid faces are more prominent. Fig. 4 (crystal No. 
5,0.9 X 0.9 X 0.5 mm.). In one case the steep pyramid 4, 20, 
with J, 96 0, were the only faces developed. Fig. 5 (crystal No. 9, 
I Xo0.5 0.6 mm.). Fine horizontal strize were then apparent on 
all faces of the crystal. Rounded transitional faces between vand ¢ 
were noticed on one crystal. 
Of the measured crystals No. 1 (with the observed forms c¢, 2, J, 2), 
No. 7 (with ¢, v, ~, 4), No. 10 (with c, v, f, 6), No. 12 (with ¢, 2, 
