52 CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. [bull. 167. 
biotites 45 a and 46 a . The pyroxene 21 a shows, however, practically 
the same amount as its mother rock, the syenite-lamprophyre 21. 
In most of these cases, notably the last one, the vanadium in the 
separated mineral is not sufficiently in excess of that in the rock from 
which it was taken to account for all of that found in the latter. Hence, 
if the determinations are correct it must also be a constituent of some 
other mineral than the one analyzed. In roscoelite the trivalent con 
dition of vanadium corresponding to the oxide V 2 3 is now recognized 
as probable, although Roscoe's analysis reports V 2 O s and Genth's an 
oxide intermediate between V 2 3 and V 2 5 . This assumption seems to 
be necessary if the mineral is to be regarded as a mica, and it is then 
doubtless the equivalent of trivalent iron or aluminum. It would then 
be natural to look for it in the aluminous or ferric silicates of igneous 
rocks, certain biotites, pyroxenes, and hornblendes, and its absence in 
such minerals as serpentine and chrysolite, as shown by analyses 3 and 
60, appears natural enough. 
Few and inconclusive as the above comparisons are, they seem to 
favor strongly this view as to the source of the vanadium, and in a 
measure are confirmatory of the observation of Hayes (Proc. Am. Acad. 
Arts Sci., Vol. X, 1875, p. 294), who rather indefinitely associates it with 
phosphorus and proto-salts of iron and manganese, which are usually 
more prominent components of basic than of acid rocks. 
We are probably justified by the evidence in tabulating the vana- 
dium as V 2 3 in analyses of igneous and some metamorphic rocks which 
have undergone little or no oxidation, but with sandstones, clays, lime- 
stones, etc., which are of more or less decided secondary origin, this is 
probably not the case. The probabilities are there largely in favor of 
its acid character and the existence of various vanadates of calcium, 
iron, aluminum, etc., in which case it should appear in analytical tables 
asV 2 (V 
1 In the regular course of analysis vanadium will be weighed with alumina, iron, titanium, etc., 
since it is precipitated by both ammonia and sodium acetate in presence of those and other metals, 
hence the alumina percentages in nearly all rock analyses heretofore made are subject to correction 
for the vanadium the rock may have held. This correction is of course to be made in terms of V 2 6 
and not of V 2 O a . 
All determinations of iron are likewise affected by its presence, whether as V 2 5 or V 2 3 . As V 2 3 
it will make the FeO appear too high in the proportion V 2 3 : 4FeO, or 150.8:288, an error which 
becomes appreciable in some of the basic rocks and amounts to 0.25 per cent in the biotite 23". As 
V 2 6 the FeO will not be affected, but in either condition the Fe 2 3 will need correction and to a 
different extent, according as the titration of iron is made after reduction by hydrogen sulphide or by 
hydrogen. If the former is used, as should always be the case in presence of titanium, the vanadium 
is reduced by it to V 2 4 , which in its action on permanganate is equivalent to 2 molecules of FeO 
representing 1 of Fe 2 3 , or only one-half as great as the influence on the FeO titration of the same 
vanadium as V 2 3 . An example will make this clear: 
Found 2.50 per cent apparent FeO in a rock containing 0.13 per cent V 2 3 . 
Deduct 0.25 per cent FeO, equivalent in its action on KMn0 4 to 0.13 per cent V 2 3 . 
Leaving 2.25 per cent FeO corrected. 
Found 5 per cent apparent total iron as Fe 2 3 in the same rock. 
Deduct 0.14 per cent Fe 2 3 , corresponding to 0.13 per cent V 2 3 . 
Leaving 4.86 per cent corrected total iron as Fe^0 3 . 
Deduct 2.50 per cent Fe 2 3 , equivalent to 2.25 per cent FeO. 
Leaving 2.36 per cent Fe 2 3 in the rock. 
Failure to correct for the vanadium in both cases would have made the figures for FeO and Fe 2 3 , 
respectively, 2.50 and 2.22 instead of 2.25 and 2.36 as shown above. 
