230 
MANGANESE DEPOSITS OF INDIA : MINERALOGY. [ PaRT 1 : 
Before making use of the foregoing table it is usually necessary to 
obtain pieces of the mineral to be identified free 
Remarks on the fore- . , . -.i ,i • i tt n 
going key. from admixture with other minerals. Usually 
the ores are sufficiently coarsely crystalline for this 
to be simply a matter of breaking up the ore into fairly small pieces 
and carefully selecting those fragments that under a lens are seen 
to be pure. Sometimes, however, the granules or crystals of the 
minerals composing an ore are too small to be conveniently sepa- 
rated in this way. If the ore is evidently a composite one it is then 
necessary to resort to methods of separation that it will not be possi- 
ble to discuss here. Having obtained a portion of the pure mineral, the 
first test according to the table is to try and scratch it with a penknife. 
If the mineral can only be scratched with doubt or not at all, then it is 
probably one of the minerals in the left-hand portion (I) of the table. 
It must be noticed that although hoUandite is grouped with the minerals 
that can be scratched it is often not possible to scratch its crystal faces, 
its true hardness being probably about 6 ; but if a knife be drawn across 
the fibrous fracture of the mineral it will be easily scratched. Hence I 
have placed hoUandite \vith the scratchable minerals. Most psilomelane 
is not appreciably scratched by a knife ; but it is sometimes quite 
soft and therefore the mineral is placed in both sets of minerals 
(I and II). The soft varieties are sometimes only to be distinguished 
from wad by quantitative analysis, when psilomelane will be fomid to 
conform to the manganate formula given in the key, whilst wad wiU be 
found to be an indefinite mixture of oxides. The test for the presence 
of silica (Si02) is made by dissolving the mineral in hydrochloric 
acid. A residue of gelatinous silica can be taken to indicate that 
the mineral is braunite ; whilst a residue of a few grains of sand or a very 
small quantity of silica can be neglected. 
It must be borne in mind that the key is not infalUble and that in many 
cases it will be found to be impossible to decide by its aid to which of two 
minerals a given specimen corresponds. There is then no alternative to 
making a complete analysis of a carefully picked specimen of the mineral. 
It is, for example, often a matter of the greatest difficulty to decide 
whether a particular specimen is pyrolusite or manganite. This is due to 
the fact that manganite changes into pyrolusite, and that specimens may 
be obtained in which this change has not been completed, so that the 
specimen is intermediate in composition between the two minerals. In 
the same way it is often difficult to decide whether a particular specimen 
is to be referred to manganite or hoUandite, owing to their similar colour, 
