250 F. A. Genth’s Contributions to Mineralogy. 
Although the material for this analysis appeared to be quite 
pure and homogeneous, the already commenced alteration of this 
mineral is indicated by the low percentage of silicic acid, the 
ae age of water, etc. 
It is rarely pheno! with crystals of albite, but frequently 
with game crystals of Sennen sphene, ripidolite, gold, pyrites, 
blende, chalcopyrite and gal 
8. ane. 
The most interesting associate of the massive albite from the 
Steele mine is ripidolite, ecause it is the result of its alteration, 
as can be easily observed from the fact that, wherever the albite 
has a crack, through which water could penetrate more readily, 
a greenish line makes its appearance, which indicates ci ey? 
mencing Set ; where this has already made mo it 
can hat the ripidolite is lining both sides of f the fssu fn 
r 
nucleus of albite, often having the diminutive shape of the orig- 
ina al 
n cavities it is rarely observed in wormlike aggregations of 
microscopic erystals, sometimes in peculiar casts,* having the 
appearance of crystals, but generally in masses of aggregated 
seales of a dark olive green color. 
rof. J. D..Dana, who had the kindness to examine these casts, makes the fol- 
lowing rears ina jaa: dated New Haven . June 23, sb 
tions looking as if the cuts were due to esatben slate es that have been removed; 
. The fact that the cuts sometimes go only half way ae the preudo-ryetal ; 
. The imegularty of form presented ; for although the surfaces are flat, there 18 
nes. 
y to k 
lar prisms, they might possibly occur in one pair of the faces, but would not also on 
the others at the same time, and much less would they be found on the planes Fre 
c oreover such Pegular tinagles look ae-i the system of crys 
a was rhombohedral or monometric, while the forms are very far from 
5. Teteedarget pseudo-crystal there is a piece of the rock projecting on one 
side. paged meme piece has its pot ee for a iecaiek of nearly a line 
2 
stalline tes : 
te occupies y= cavities ; cap gr pa ver 
y marked they would chapters a the triangles alike on all the faces 
ofthe ripiolite, arg tie: ca Vicion The difficulty in this view of the case is thix— 
pode not occur on any mineral that I can suggest as he. proluble 
eae sine" They ae fxd ‘on some foliated chlorite, ripidolite, elinochlore and pyto* 
‘confess that I do not fully understand the ripidolite.” 
