160 T. Crook—Titaniferous Volcanic Rocks. 
particular case, of the simple process of crushing and magnetic 
separation as a means of distinguishing titaniferous magnetite from 
ilmenite, when these occur in rocks. It has been commonly 
considered that if leucoxene is developed among the cleavage cracks 
the mineral must be ilmenite. But it should be remembered that 
titaniferous magnetite also yields leucoxene as an alteration product; 
and it may on this account be safely asserted, that much titaniferous 
magnetite has been described as ilmenite on evidence gathered from 
rock sections alone. ‘This confusion can be readily avoided by 
following Cordier’s method of partially crushing the rock. It is 
convenient to sift, wash away the powder, and dry the residual grains. 
From these, magnetite, if present, can be withdrawn by a small hand 
magnet, whereas the ilmenite remains behind. The magnetite thus 
withdrawn is somewhat readily soluble in strong hot hydrochloric 
acid, and if the magnetite is titaniferous this can be proved chemically 
by the violet colour reaction on reduction with metallic tin.’ In view 
of the simplicity and effectiveness of this process, Dr. Washington 
should have no difficulty im determining whether the titanium of 
his rocks is present as titanite, ilmenite, augite, olivine, or titani- 
ferous magnetite. The matter is still under investigation, but 
Dr. Washington informs us that ‘the available data indicate that 
a large proportion of it is present in titaniferous magnetite, with 
probably somewhat less in the augite.” On this matter we may | 
venture to predict that further work will prove practically all the 
titanium to be present as titaniferous magnetite (and ilmenite), as 
Cordier showed about a hundred years ago. 
Now that we have attempted to do justice to Cordier, let us proceed 
to examine certain features of Dr. Washington’s preliminary notice 
which seem to call for criticism. 
On page 76 (loc. cit.) we are told that ‘‘the pale green or 
colourless augites of Central Italy are markedly titaniferous,”’ one 
of them carrying 2°85 per cent. of titanium dioxide. On looking 
up the account given by Dr. Washington in ‘‘ The Roman Comagmatic 
Region’’ to which he refers us, we find that the titanium-dioxide 
content of this augite was determined in the following manner :— 
‘‘The rock powder used for the chemical analysis of the rock was 
digested for some hours in warm dilute hydrochloric acid, to which 
a little hydrofluoric acid was added. The residue was washed out 
with dilute solution of sodium carbonate, and the process repeated, 
but without hydrofluoric acid, the final residue being, of course, 
washed perfectly free from all soluble salts. This process would 
naturally dissolve all the leucite, olivine, melilite, magnetite, apatite, 
and anorthite, which are the only other minerals present, and would 
have only a slight effect on the augite, removing the outer portions.” 
Then follows an analysis which shows 2°85 per cent. of titanium 
dioxide. 
The obvious defect of this procedure is, that ilmenite andrutile may . 
easily have been present in the powder analysed. It is a fact that 
‘The possible occurrence of coarse intergrowths of ilmenite should always be 
kept in mind, and any residue which may be obtained should be examined 
magnetically, microscopically, and chemically, as rutile may also possibly be present. 
