MINERALOGY OF BLACK LAKE AREA. 
21 
reddish-brown material being less magnetic (as well as lighter and more 
friable) than the black opaque portion. The two portions were then 
analysed and yielded the following results: 1 
Analyses of Chromite . 
Although it is not so stated in Dresser’s report, the writers are 
informed by M. F. Connor, by whom the analyses were made, that there 
was no special determination of the ferrous iron in the samples, but that 
in each case the total iron was estimated as FegO*, and the results so 
obtained then reduced to the form FeO. It is not probable, however, 
that the whole of the iron is actually present in the mineral in the ferrous 
condition, and for this reason it is impossible, from the above analyses* 
to calculate formulae to represent the compositions of the two varieties. 
All that can be said is that the black fraction is the richer in oxide of 
chromium and also of iron and aluminum, while the reddish-brown 
material contains relatively more of the alkaline earth metals, calcium 
and magnesium. In each case the presence of about 2 per cent of water, 
which is only expelled on ignition, indicates an admixture of some 
mineral containing water of constitution, and this is possibly a hydrous 
magnesium silicate, such as serpentine or clinochlore. 
hydrous oxides. 
LIMONITE. 
Yellow hydrous oxide of iron forms a thin film on weathered surfaces 
of the basic rocks, such as diabase. Earthy limonite was also found, 
as an alteration product of siderite, on the apatite specimens described 
on page 8$. 
* Op. dt. p. 78. 
In Dresser’s report the molecular ratio for MgO in the black opaque port on is given as 0*341; this 
should be 0 * 391. 
