276 =©Cross and Hillebrand—Cryolite from Colorado. 
PACHNOLITE. 
a. From the thin walls.—The microscopical examination of 
the walls and membranes produced by the first mode of altera- 
tion of the cryolite shows them to be coated by many minute 
but perfect, colorless and transparent, prismatic. crystals which 
are usually placed at right angles to the central plane of the 
wall, though sometimes in irregular manner. They reach a 
maximum length of 2™ by a thickness of 0-2 to0-4™. The 
crystals are occasionally yellow in color, while retaining their 
cryolite substance. 
Thomsenolite is but rarely present with pachnolite on these 
walls. The few crystals found correspond to the pachnolite 
size and possess a prism angle of nearly 90°, and a very perfect 
cleavage parallel to the base. ‘ 
aterial from a network of thin walls covered by pachnolite 
crystals was subjected to chemical analysis, yielding the result 
under IT. p. 281. : 
. From the bluish alteration product.—The | bluish mass 
formed by the second mode of decomposition has in great part 
a regular crystalline structure produced by a more or less per 
* Groth, Lc. p, 464. 
