K5HALLEE.] 
DUMORTIERITE. 
115 
microscope for impurities. None was found. The mineral was 
unquestionably pure. 
The general analytical methods used were those pursued in the 
Survey laboratory for silicate analyses, with a few modifications. The 
mineral was fused with sodium carbonate, the silica separated and 
re-fused with sodium carbonate. The silica was filtered off, weighed, 
and treated with HF, which left some residue. The alumina (plus 
iron and titanium) was precipitated three times to be sure of remov- 
ing all of the sodium salts. It was ignited and weighed with the 
silica residue, fused with sodium bisulphate, some silica recovered, 
the iron was reduced and determined by titration and the titanium 
was determined colorimetrically. The presence of titanium was sus- 
pected from the color of the pleochroism of the mineral. The boric 
acid was determined by the Gooch method, using all of the known 
precautions. The mineral was twice fused with sodium carbonate and 
the boric acid was finally weighed as calcium borate. The water was 
collected in a calcium chloride tube, the mineral being heated in a 
Gooch tubulated crucible in the usual manner. A blank determina- 
tion was run before and after each water determination and a small 
correction applied. All possible precautions were taken throughout 
the analysis, which was made in duplicate. The results are given 
below. 
Si0 2 . 
A1A 
TiA 
FeA 
H A 
BA 
28.58 
63. 31 
1.49 
.21 
1.53 
5.21 
28.78 
63. 30 
1.40 
.25 
1.51 
5.53 
100. 33 100. 
Average. 
28.68 
63. 31 
1.45 
.23 
1.52 
5.37 
100. 56 
The titanium is regarded as present as Ti 3 0. n replacing the alumina. 
Combining the alumina, titanium, andiron, the following ratios are 
obtained: 
Si0 2 5.94 . >r «; 
A1A 8.00 8 
BA 1-06 L 
H 2 96 1 
The formula for dumortierite then is 
8A1A, UUXp 1H 2 0, 6Si0 2 . 
It has not been proved that either boric acid and alumina or boric 
acid and hydroxyl may mutually replace each other in minerals as Huor- 
