Chap. X.] the identification of manganese minerals. 
225 
nese, the depth of colour obtained with two minerals, under the same 
circumstances as to relative quantities of mineral and fluxes, being 
an indication of the relative amoimts of manganese present in the two 
minerals. The green colour is due to the formation of manganates 
of sodium and potassium. This is the most useful of the tests and the 
one that is most generally applicable and gives the result desired in 
the shortest time. The third test is one that is even more delicate than 
the fusion test. It is known as Volhard's test and consists in obtain- 
ing a nitric acid extract of the mineral under examination and boiling 
it with lead peroxide. Any manganese present is oxidized with the 
formation of violet or red permanganic acid, the colour being very similar 
to that of potassium permanganate. This test is only directly applicable 
to minerals that dissolve in acids. It is best to dissolve the mineral 
direct in nitric acid if possible. If the mineral has to be dissolved in 
hydrochloric acid, it is necessary to take the solution nearly to dryness to 
remove the hydrochloric acid ; for any quantity of this acid prevents the 
formation of the colour. If the mineral be a silicate it is not as a rule 
decomposed by acids, so that a fusion is first necessary ; and then the 
green colour will probably be obtained in the course of the fusion render- 
ing the application of Volhard's test unnecessary. Hence this test is 
only conveniently applied in the case of minerals that are soluble in 
acids. It has the advantage over the fusion test that it enables one to 
detect the minutest traces of manganese, such for instance as those to 
which the colour of rose-quartz may be supposed to be due. 
We can now pass to the dark-coloured minerals, which usually possess 
^ some sort of a metallic lustre. The colours 
uiinerals.*^*^ " ^" ^ shown by these minerals are some shade of black, 
steel-grey, dark blue-grey, brownish-black, or 
bronze-black. Owing to the fact that there are several fairly common 
minerals that may be at first sight confounded with manganese-ores, I 
wiU also take them into consideration. Supposing that one has found 
a [piece of a black, or dark grey, or allied-coloured, mineral of consider- 
able weight, it may be either a manganese or iron mineral, or chromite, 
or pitchblende, as well as various other minerals of great rarity found 
but rarely or not at all in India. The first test to apply is to powder 
the mineral, when the colour of the streak becomes evident. The 
following table shows the way in which the mineral can be either identified 
as one of the minerals, hematite, magnetite, ilmenite, pitchblende, or 
chromite, or else separated off as an ore of manganese, the test that 
decides whether the mineral is a manganese mineral being the fusion test 
