Cross and Hillebrand—Cryolite from Colorado. 285 
purest, finest kaolin being especially remarkable. ° Examined 
microscopically, gearksutite is seen to consist, as stated by Prof. 
Groth, of exceedingly minute colorless needles, the average 
length of which is less than 0-°02™", and the thickness less than 
0-002", and apparently possessing oblique extinction. 
Chemical investigation.—Gearksutite was found by Hagemann 
(I. c.), to possess the following composition: 
Gt yeas 15°52 
Ugo eee 19°25 
2 f geculspee 2°4 
HO. 20°22 
F 41°18 
98°63 
An examination of the above results shows that the atomic 
ratio of Al: Ca+Na,: FI is 1:1:4, instead of 1:1:5 which 
would represent complete saturation and require about 12 per 
cent more fluorine than was found. On the assumption that 
the missing fluorine is replaced in the mineral by oxygen or 
Connection with the determination of the fluorine, or water, or 
both, in consequence of which the construction of a satisfactory 
formula has heretofore been impossible. 
The material for the following analyses was first partially 
crushed, then freed from admixed heavier particles of foreign 
Matter by triturating in a beaker with water, the impurities 
falling to the bottom of the vessel, while the light gearksutite 
remained suspended in the liquid and was removed by decan- 
tation. By repeating this operation a great many times, a pro- 
duct was finally obtained entirely free from all foreign admix- 
ture. It was ‘allowed to settle completely, the supernatant 
liquid poured off and the residue dried first on the water bath, 
then at 100 : . ° 
a. db. Mean 
y Gees oe enn 15°33 15°30 15°31 
OR ek ee 92-29 92°32 22°30 
Neo O1 aaa 0°10 
) Sat aE a 0°04 ee 
13 9 Seal ge toe 15°5 15°39 15°46 
Bo 42-14 42°01] 42-07 
95°44 ce 95°28 
Loss as oxygen ..4°56 / eos od 
100-0 100°00 
