"278 Cross and Hillebrond—Cryolite from Colorado. 
various individuals have perfectly developed crystal faces. In 
some minute cavities a few crystals with quite perfect termina- 
tions were found, and upon these some faces were sufficiently 
as —3°3 (811). They are all twinned parallel to 7-7(100) and 
the low projecting angle upon O is sometimes distinctly visible. 
The angles given in the following table are all means of 
numerous closely agreeing measurements, and demonstrate the 
erystallographical identity of the mineral under discussion with 
pachnolite : 
Angle. Crystal a. | Crystal b. Pe oor Ae Calculated. 
wad (04 100) oo... Si" 10°) Oi" 49" | Gl" 18) Si ee 
24, OF10~ 001) 50.2 90°21” | 90°21’ | 90° 207 
~ O(111. 001 -._..- 116° 39’ | 116° 30’ | 116° 30° 
—3°3 . —3°3 (311.311 ~| 138° 45” 138° 45” | 138° 52’ 14’ 
—3°3 .1(311 . 110). ___. 149° 03” 149° 17.19 
0 0 (001 . 001) twin -. 179° 21’ p aie! 30 
The face —3:3 was observed on a number of distinct twin 
wholly absent from the material analyzed. 
e second specimen (B), from which especially good mate- 
rial was obtained, had a seam 2™ thick of coarse Sip 
a 
rystal- 
line grains of pachnolite were exposed, with the regular arrange 
snk dames Actual disscuach of crystal faces other 
than the prism is rarer than in specimen A, but the size h 
grains, reaching 5™ in length by 1-8™™ in thickness, 1s sue 
as to admit of the preparation of.thin sections for ye — 
ination, and also gave absolutely pure material for chemical 
