G. J. Brush on Boltonite. 395 
When the polarization is elliptical a colored cross it is true 
will be seen and it will revolve with the analyzer and change in 
tint, but at angles of 180° it becomes normal and nearly black. 
Of course ght occurs in every state of polarization, passing 
from elliptical through circular to plane, according to the relative 
dimensions of the axes of the ellipse, but after some practice it 
possible by means of the cross to judge of these dimensions 
approximately. 
Troy University, Dec. 25th, 1858. 
Arr. XLV.—On Boltonite ; by Prof. Gxo. J. BRUSH. 
Tux identity of this mineral with chrysolite was pointed 
out by Professor J. Lawrence Smith in this Journal, vol. xviii, 
p. 372 (November, 1854). Previously to this Dr. Kenngott* 
es made by v. Hauer that 
ubsequently + een 
’s an he 
lorie acid; afterwards great care was taken in ch 
ng Sis the purest of the fragments thus treated. Three analy- 
made upon specimens so selected gave: 
7 Ignitio 
1 42°56 51°77 85 010 9222 = echt 
% 41-95 51-64 3-20 0:25 ge homage 
2°41 50°06 C not. 
: gangue, but analyzed a specimen 
by pane. Tn his first patie y the mineral was decom 
fusion with carbonate of soda. His results gave— 
* i 
Mineralogische Notizen, Zwélfte Folge (March, 1854). 
a Det Se ‘ , late mi e olge Forschungen im Jahre, 1854. Leip 
e 
‘ 
