62 
Simpson — Contributions to Mineralogy of W.A. 
1'hc ratio of Fe^Ou to MoO;j for the unusually clean Mulgine 
mineral is (A) 1:3.90. This is close to the ratio 1:4 given for the 
artificial compound. Schallcr’s ratios are nearer 1 :3, but his 
material may have contained limonite, which is a frequent 
associate. 
The formula for ferrimolybdite drawn from these figures is 
FcT):{.4'vloO:i.5H20H-5H20. This differs somewhat from previous 
suggestions (Fe20;j.3MoO;^.7^Il20, Schaller), 
The Mulgine mineral is insoluble in water, but is readily dis- 
solved by warm hydrochloric acid, and slowly decomposed by 
warm ammonia water, MoO^ going into solution and the iron 
being converted into ferric hydroxide. Remembering that ferri- 
molybdite is an acid salt, these facts point to the genesis of the 
mineral in weakly acid ferruginous w^aters resulting from the 
simultaneous weathering of pyrite and molybdenite. Secondary 
powellite on the other hand results from the weathering of 
molybdenite in the presence of alkaline calcareous waters. 
The physical properties of the Mulgine mineral are as 
follow: — Density, 2.99. This agrees with Schaller’s figure for the 
mineral from Hortense, Colorado. Hardness, small but indeter- 
minable owing to the extreme fineness of the fibres and their 
almost complete lack of cohesion. The colour in mass is identical 
with Ridgways 23 d, picric yellow. Under the microscope the 
fibres are perfectly transparent and of a pale yellow colour at 
right angles to the elongation. Parallel to it the absorption is 
very marked, the thicker fibres being dark yellowish green and 
almost opaque, the thinner ones a lighter green. 
After partial deliydration to a light green colour caused inad- 
vertently l)v mounting in hot balsam, the absorption parallel to the 
filu'es is complete in thicker fibres, which appear quite black, 
changing to yellowish green across the fibres. The marked 
plccchroism is referred to l)y Lacroix in describing the mineral 
from Corsica, and by Schaller in describing the United States 
specimens. The extinction is in all cases parallel, and the birC' 
fringence high, with Z parallel to the elongation. 
(4) Kyanite, Cluttering Valley, S.W. Div. 
Kyanite has been found in several places in the gneissic 
granite ranges north of the junction of the Chittering Brook and 
the Swan River. The three occurrences here described all lie 
between Lat. 3U and 32« S. and a little east of Long. 116° E. 
Loii'cr Uiiiicring.—VhQ first known occurrence is on the south 
side of a small valley tributary to the Chittering Valley east of 
