Chap. III. ] 
SiANGANMAGNETITE. 
39 
specimen investigated by Dr. Holland was strongly magnetic, showing 
distinct polarity, and otherwise exhibiting the properties of mag- 
netite, except that its streak was reddish brown instead of black. 
In mv examination of the manganese-ore deposits of the Vizaga" 
patam district I found that what was apparently manganmagnetite is 
rv not at all uncommon. The difficultv is 
Occurrence. 
to avoid confounding it with braumte, 
for, as is explained on another page (63), this mineral is also 
magnetic, although to a much smaller degree. Both minerals have a 
lustrous black conchoidal to sub-conchoidal fracture, but braunite 
usually exhibits a well-marked octahedral cleavage not shown by mangan- 
magnetite. When in small grains, however, the cleavage of the brau- 
nite may be difficult to develop. In this case if the luineral be not 
strongly magnetic it may be taken to be braunite. but it is best to 
confirm this deduction as to the character of the mineral by making 
a chemical test. The best is to treat the finely powdered mineral with 
strong hydrochloric acid. If the mineral be braunite it will leave a 
residue of gelatinous sihca : whilst if it be manganmagnetite it \vill 
either dissolve completely, or it wiU leave only a very small residue due to 
mechanically included silica, which will not be gelatinous. If the mineral 
contain only a small amount of manganese, this will of course 
show that it is not braunite ; but the prese»Mie of a large amount of 
manganese does not necessarily mean that the mineral is braunite. for 
there is another magnetic mineral, vredenburgite. that contains a 
high percentage of this element. The deposit at which I found mangan- 
magnetite in the greatest abundance is Garbham, but I also foimd it 
at Kodur and Avagudem. At Garbham it occurs in two ways. One 
is in a rock composed of manganese-garnet (spandite) with some 
apatite and a little mica (rich brown), in which the manganmagnetite 
fomis perhaps one-third of the rock. The grains of manganmagnetite 
are I to ^ inch in diameter, ^\^len freshly fractured they are seen 
to be traversed by rather numerous thin veinlets of psilomelane. To 
test if the mineral were really manganmagnetite, containing the mangan- 
ese in combination as a part of the molecule, was therefore a matter 
of some difficulty. After a lot of trouble some pieces were picked out 
that had fresh fracture surfaces on every side and showed no trace of 
the psilomelane veinlets. These were found to give decided reactions 
for manganese indicating its presence in appreciable ciuantitv. but not 
in large amount. I must confess that I do not feel absolutely certain 
that any of the pieces tested were really quite free from psilomelane 
