78 
CONTRIBUTIONS TO MINERALOGY. 
[BULL. 261 
Both of the preparations were perfectly white. The microscopic 
examination showed thallium analcite to be mainly isotropic, with a 
few crystals having double refraction, as was the case with the silver 
derivative. The thallium compound is easily decomposed by nitric 
acid, giving- sandy silica. 
Deducting from analysis F analcite equivalent to 0.12 per cent of 
Na.,0, and reducing to 100, the analysis becomes: 
Si0 2 
A1 2 
T1 2 
Residue F. 
32.61 
13.60 
53. 79 
100.00 
Theore 
T1A1S 
31.33 
lOO.Ot 
In the second column is given the calculated percentage composi- 
tion of normal thallium analcite. 
The molecular ratios of F are 
24T1 2 0, 23A1 2 3 , 100SiO 2 . 
A closer agreement with theory could hardly be expected. 
In the case of the silver compound, the one molecule of water o 
the original mineral has been retained, and it is essentially analcit 
with silver replacing sodium. It is not so with the thallium derivai 
tive, nor with the ammonium compound of the former investigation? 
In both of these derivatives the water of the original mineral was lost 
the formula being that of leucite with thallium or ammonium replao 
ing potassium, leucite being a mineral closely related to analcite. 
One crude experiment was made to show the action of lead nitral 
on this mineral. Natural analcite was heated in a sealed tube with ij 
10 pei - cent solution of lead nitrate for six hours at about 200 (J. Tl 
composition of the washed and dried residue follows: 
Si0 2 . 
A1 2 3 
PbO . 
Na 2 
H 9 0. 
Molcciila 
r.iiios. 
60. 34 
100 
17.55 
17 
14.75 
< ! 
6. 03 
< 
• 
undet. 
98. 67 

