220 
MANGANESE DEPOSITS OF (NDIA : MINERALOGY. [ ParT I 
turn is idiomorphic towards the quartz. Until these arsenates have 
been analysed quantitatively it wiU not be possible to say if they 
correspond to any known species or are new minerals. 
It is probable that these arsenates are commoner than is suspected. 
For it must be noticed that under the microscope 
Distinction of arsenates, xi. l. j. i-ii.i-j.i_ 
apatite, and barytes. ^"-^7 0"en present a great resemblance to both apa- 
tite and barytes. All these minerals as seen 
under the microscope are colourless, with a high index of refraction 
giving rise to a highly pitted surface. They all show cleavage?, and, 
except in the case of the Kajlidongri arsenate, low polarization colours ; 
and the tendency is for them all to be called apatite if they are seen 
only under the microscope. Nevertheless, it is comparatively easy to 
settle which mineral it is that is present, if the quantity be not too small. 
In the first place if it be very finely powdered and treated with hot 
dilute hydrochloric or nitric acid, both apatite and arsenates will pass 
into solution. It is not then sufficient to add ammonium molybdate 
to the nitric acid solution and assume that the yellow precipitate 
indicates a phosphate and therefore apatite. The solution should be 
first treated with a solution of sulphurous acid to reduce any arsenate 
if present and then a current of sulphuretted hydrogen passed ; if a 
yellow precipitate be formed, it may be assumed that the original rock 
contained arsenic, probably in the form of arsenate. If no precipitate 
be formed in this way then the molybdate cest may be apphed and the 
yellow precipitate then obtained taken as evidence of the presence of a 
phosphate, presumably as apatite. If neither an arsenate or apatite be 
found to be present it will then be as well to make a test for barium by 
fusing up a portion of the rock with fusion mixture and testing the 
acidulated extract of this for barium. When the minertil is macroscop- 
ically visible it is a much simpler matter to prove the presence of either 
an arsenate or barytes. The arsenic mirror obtained by heating the 
mineral with sodium carbonate and potassium cyanide in the closed tube 
will serve as a good test for the arsenate, whilst the green flame and the 
blackening of a silver coin will serve as tests to prove the barium and 
sulphur present in barytes. 
I have found barytes in the rocks of the gondite series, apparently as 
„ an original constituent, at three localities. For the 
Baryte.s. 
reason that it may be easily overlooked if one is noc 
on the lookout for it, it is probable that this mineral is much more 
frequently present in the rocks of this series than I have detected. If its 
