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MANGANESK DEPOSITS OF INDIA : MINERALOGY. [ PaRT I t 
for any known mineral. Similarly tlie manganese-micas show various 
shades of pink, delicate green, orange, and lilac-brown, ia thin scales 
examined imder the microscope. As other examples of the effect on 
the colour of a mineral may be mentioned the manganese-epidote, pied- 
montite, and the manganese-sphene, greenovite. Excepting the oxides, 
which are usually of some shade of black or dark grey, the minerals of 
manganese usually show some variety of blue, pink, lilac, or crimson, 
whilst orange and yeUow tints are found in the garnets. Other colours, 
such as green and brown, are also found in manganese minerals, but 
they are of much rarer occiu'rence. The colour of a given miueral 
depends, of course, on the other constituents besides the manganese, 
so that it is difficiilt to say which colours are specially due to the man- 
ganese. Thus in winchite and blanfordite, mentioned above, the soda 
present has perhaps partly contributed to the colour. But a com- 
parison of the colours of minerals containing mangan^ese with those of 
minerals otherwise similar but practically free from this constituent 
points to the fact that the colours specially due to the presence 
of manganese in a mineral are red, pink, and lavender, and allied tints. 
Rose quartz and amethyst may also be cited as exhibiting in a remark- 
able manner the colour ef?ects produced by manganese ; for both these 
varieties of quartz have been shown to contain this element i. 
As regards mode of occurrence manganese minerals exhibit the 
greatest variety ; for they are found in igneous, 
The occurrence of , -i- it x i j- - i 
manganese minerals. metamorphic, and sedimentary rocks, and m mmeral 
veins traversing these rocks, as original minerals 
formed at the same time as the enclosing rock or vein-filling. In all 
these rocks and veins they may also be foimd as secondary minerals 
formed by the chemical alteration of pre-existing minerals in the rocks 
or veins, or by the introduction of manganese salts in solution from 
without. Moreover, by the weathering of these minerals when they 
are exposed at the surface secondary manganese minerals are frequently 
formed. The minerals most frequently foimd are the oxides, which 
occur in metamorphic and sedimentary rocks and in veins, and per- 
haps rarely in igneous rocks^. The carbonates are not found in 
igneous rocks, but are found in all the others. Silicates are especially 
characteristic of the metamorphic rocks ; they are foimd somewhat less 
1 Rose quartz, see page 212; amethyst, siee SL Berthelot, Comptesr endues, CXXXXIII, 
pp. 477 to 488, (1906). 
2. O. A. Derby has ascribed an igneous origin to an ore or rock composed of polianite 
(Mn02) and speseartite-gamet. Aif tr. Jour. Sci., XII, pages 26 , 30, (1901.) 
