92 CONTRIBUTIONS TO MINERALOGY. [bull 
able quantity of it in a pure condition. At the California locality 
mineral occurs in large, pure masses, very favorable for chem 
investigation. From an analysis made by the writer on the Califoi 
material, a formula was deduced in which the boric acid and w;i 
have a certain fixed value. The other analyses are discussed, an< 
is shown that they all agree fairly well with the new formula propo 
by the writer. An analysis of the Washington dumortierite is. i 
given. Ford tested the French material qualitatively for boric s 
and obtained a strong positive reaction. 
While a more or less complete study of the mineral has been ma 
it is fully realized that in no sense can the work be called compL 
The material for crystallographic study was poor, and it is very m 
hoped that better crystals will at some future time be found. r 
determinations of optical constants are very meager, for the us 
condition of occurrence of the mineral is not favorable to such stu 
Only a few analyses are available for an} T discussion of the composil 
of the mineral, and -though dumortierite does not contain a large m 
ber of constituents, many more analyses — but only extremely accui 
and reliable ones — will be gladly welcomed. 
It was found that the California material differed somewhat in 
properties from normal dumortierite. The color is lavender inst 
of blue, the pleochroi'sm is colorless to red purple instead of blue, 
the mineral contains 1^ per cent titanium oxide. It is of especial in 
est to correlate these differences, as it adds another good example 
that class of silicates which contain a small amount of titanium 
(seemingly thereby) acquire a purple pleochroism. 
OCCURRENCES. 
FOREIGN. 
FRANCE. 
Dumortierite a is found at several places in the vicinity of Ly 
(Rhone), where it occurs in a pegmatite gneiss. At Beaunan, on 
road from Oullins to Chaponost, it is found in a small quarry in gn 
in slender blue libers in the midst of veinlets or lenses of feldspar 
pegmatite. At Brignais it occurs in very small fibers disseminl 
throughout a white pegmatite, associated with large black tourmalh 
garnets, muscovite, and cordierite, the latter being largely altered 
mica. In some cases bluish tourmaline and dumortierite have the\ 
tical axis in common. Pseudomorphs of mica after dumortierite 
frequent. 
The mineral has a good cleavage parallel to a {100} and an iml 
feet prismatic one. There are also "planes of separation" paralle 
the base. Twins, 'analogous to those of aragonite, are frequent. 
a Lacroix, A., Mineralogie de la Franc, vol. 1, 1893-1895, pp. 15-19. 
