Chap. XVII. ] gondite series : alteration. 
355 
The rhodonite-bearing rocks indicate the same direction of change. 
Alteration of When the rhodonite is coarsely crystalUne, a 
riiodointc. microscope section often shows hnes of alteration 
extending along the cleavage planes of the mineral, and thence 
spreading out to form networks and patches of ore. The appearance 
seen is like that shown in figure 4, Plate 12, although this is actually 
a photo of a pyroxene from the Vizagapatam district. This can be 
taken as conclusive evidence that, in the case of the rhodonite also, 
the direction of change is from sihcate to ore, and not the reverse. 
Time of Altepation of the Manganese-silieate-roeks into Manganese- 
ores. 
As there is, hence, little doubt about the direction of change in 
these rocks, we can now inquire when the alteration took place. On 
page 321 I have already mentioned a case of the inclusion of manga- 
nese-ore in Archajan granite, and the possibiUty that this indicates that 
the alteration of silicate to ore took place, at least in part, in Archaean 
times. It is of course not possible to say if this also apply to the 
Central Pro\Tnces. It is interesting to note, however, that many of the 
deposits, such as Mansar, shoAving spessartite-bearing rocks in every 
Hill deposits are Stage of alteration to manganese -ore, crop out in 
dry. the form of small hills, which on being quarried are 
found to be remarkably dry and free from water. From this consider- 
ation alone I should say that the alteration is not now taking place in 
such deposits, except, perhaps, for a certain amoimt of surface oxidation. 
In the case of the deposits that are buried in the alluvium it is difficult 
to Bay if the change is still going on or not. Probably it is to a small 
Highest points of a extent, considering that there is usually a free 
gondite band consist influx of water int^ deposit. It is a notice- 
of manganese-ore. ^^^^ ^^^^^ howeve.^i chat if one traces a band of 
the gondite series along its strike it is usually fomid to reach its highest 
point in places where there are bodies of workable ore, the rock in 
between consisting of one of the varieties of manganese-silicate-rock, witn 
much less or practically no associated manganese-ore. This is weii seen 
in cases where the manganiferous band crops out continuously above the 
surface ; e.g. at Mansar, where the most valuable portion of the deposit 
also forms the highest portions of the hill-range in which the band is 
situated ; or at Kandri where the rock forming the saddle between North 
and South hills is composed of gondite, whilst the hills them- 
selves contain fine bodies of workable ore ; or at Ramdongri, 
II i3 
