224 
MANGANESE DEPOSITS OF INDIA : MINERALOOY. [ ParT I : 
Rhodochrosite ; easily scratched by a knife ; effervesces with hot 
dilute hydrochloric acid ; sometimes nearly white and always paler 
than rhodonite (page 122). 
Red, orange-red, orange-brown, orange, and yellow. 
Manganese-garnets ; characterized either by definite crystalline or by 
granular form, being nearly always equidimensional in all directions ; 
isotropic character under the microscope (page 161). 
f Manganese-pijroxenes ; in the Vizagapatam district are some red-brown 
to orange-brown pyroxenes not to be distinguished from garnets except 
under the microscope, when they are seen to be anisotropic (page 1.37). 
Yellow pijroxenes and amphiboles ; there are also yellow manganese- 
pyroxenes and amphiboles ; the former can only be determined micro- 
scopically (page 132) ; the amphibole is usually known by its fibrous 
or asbestiform character, whilst it may also be brownish or greyish in 
colour (page 147). 
Blue 
Winchite (page 149). 
Green. 
Phosphates and arsenates ; for distinction between these see page 220. 
All the foregoing minerals will react for manganese except the arsen- 
ates. The best tests for manganese should be 
Tests for manganese. , ^ x m, 
known to every prospector tor manganese. Ihey 
.'re three in number. A very useful one is to make a borax bead on a 
platinum wire, in the way described in most books on determinative 
mineralogy, and introduce a little of the powdered mineral into the bead. 
If the bead is heated in the oxidizing name, the presence of manganese will 
be indicated by an amethystine colour, which may become deep red if 
much iron be also present. If the bead is not too strongly coloured it will 
become colourless when heated in the reducing flame, owing to the reduc- 
tion of the manganese to the manganous condition. This test works very 
well with minerals, such as oxides, that are easily broken up in the bead ; 
but with silicates, such as manganese-garnets, the colour is not obtained 
quite so readily. The second and the best test is to fuse a small portion of 
the powdered mineral with a little nitre and fusion mixture or ordinary 
soda in a platinum crucible, or on a piece of platinum foil bent into the 
shape of a boat. The presence of manganese in quantity is indicated by a 
rich green colour ; under certain circumstances the colour is greenish blue, 
usually when the quantity of manganese is not very large. This is a 
very delicate test and serves to detect very small quantities of manga- 
