274 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE _ [VOL. XI 
yellow, and occurs as an earthy powder, in crustations, fibrous masses, 
or capillary crystals in radiating groups. For many years molybdite 
was thought to agree in composition with the artificial molybdic trioxide 
obtained by oxidizing molybdenite, and most of the present text-books 
on mineralogy persist in this error, giving its composition as MoQs. 
Iron, however, is an essential part of the mineral. Molybdite by its 
colour often calls attention to deposits of molybdenite which otherwise 
might be unnoticed. 
Tests: Heated in an open tube, molybdenite gives off sulphurous 
fumes, and a pale yellow crystalline sublimate of molybdenum trioxide 
(MoOs) is formed. Before the blow-pipe molybdenite is infusible, but 
imparts a yellowish-green colour to the flame. On charcoal in the 
oxidizing flame, pulverized molybdenite gives a strong odour of sulphur 
dioxide, and the charcoal is coated with crystals of molybdic acid, 
which appear yellow when hot and white when cold. Near the assay 
the coating is copper-red, and if the white coating be touched with an 
intermittent reducing flame it assumes a beautiful azure-blue colour. 
Molybdenite is decomposed by nitric acid, leaving a white or greyish 
residue (molybdic oxide). 
Occurrences and Accompanying Minerals: Probably three-quarters of 
the reported occurrences and practically all of the commercial deposits 
of molybdenite so far discovered are in acid rocks, such as granite, peg- 
matite, and syenite, the mineral being notably at home in rocks of this 
type. Outside of the gangue-forming minerals, such as quartz, felspar, 
mica, garnet, calcite, fluorspar, etc., the minerals with which molyb- 
denite is most frequently associated are molybdite (its alteration 
product), pyrite, pyrrhotite, chalcopyrite, malachite, chrysocolla. 
Other accompanying minerals are native copper, cuprite, chalcocite, 
bornite, tetrahedrite, azurite, galena, sphalerite, arsenopyrite, mag- 
netite, limonite, wolframite, hiibnerite, scheelite, cassiterite, and _bis- 
muthenite. 
Wulfenite: Wulfenite is a molybdate of lead (PbMos), and theoreti- 
cally contains 26.15% molybdenum, and 56.42% lead. It is heavy and 
brittle, sub-transparent and sub-translucent, and has a resinous or 
adamantine lustre, and generally a wax or orange-yellow colour. It 
may, however, be green, grey, brown, nearly colourless, or orange to 
bright red. The streak is white. The hardness is 2.75 to 3 and the 
specific gravity is 6.7 to 7. Wulfenite crystallizes in the tetragonal 
system, the crystals commonly being square and tabular and sometimes 
extremely thin. The mineral generally occurs in well crystallized forms, 
but also in coarse or fine-grained masses. 
