Chap. XVT.] 
GOKDITE SEBIKS : PETROLOGY. 
343 
The pyroxene showing the beautiful type of pleochroism in pink, 
blue, and lilac, has not been found in the typical 
rocks of this series as given in the list on pages 329 
and 330 ; but it is a rather frequent constituent of the manganiferous 
micaceous schists associated with the gondite series in Xarukot and 
Jhabua and with the winchite-bearing rocks in Jhabua. 
The manganiferous micaceous schists are not of sufficiently frequent 
occurrence to be further discussed here, but it will be as weU to give a 
short account of some of the quartzites associated with the rocks of the 
gondite series. 
A rock very frequently met with in the manganese-ore deposits of 
the Central Provinces is a black fine-grained 
Black quartzite. . .... ^ . , 
quartzite. which is somewhat heavier than an 
ordinary quartzite and usually occurs interbanded with manganese-ore, 
for which it can, at first sight, often be mistaken. Under the 
microscope it is seen to owe its peculiar characters to the presence of a 
large number of minute inclusions. The rock itself is very fine-grained, 
consisting of a quartz mosaic through which are scattered clouds of tiny 
black bodies. These are e%'idently minute crystals of some definite 
mineral, for they are seen with a high power to be prisms or rods that 
show in cross sections as little rounded or polygonal bodies. Since the 
rock when powdered and fused with nitre and fusion mixture gives a 
fairly strong reaction for manganese, it is probable that these inclusions 
consist of some manganese mineral. Plate 13, fig. 1 shows a photo- 
micrograph of a specimen of this rock from Balaghat. In this section 
the inclusions are especially abundant ; but specimens can be found 
showing every gradation between this rock and quartzite practically 
free from such inclusions, there being a corresponding gradation in 
colour from black to white. Such rocks are to be regarded as the pro- 
ducts of the metamorphism of arenaceous sediments containing varying 
amounts of admixed manganese oxide ; for, considering the intimate way 
in which the little idiomorphic prisms are scattered throughout all the 
grains of quartz, it is not probable that the manganese oxide has been 
introduced subsequent to the formation of the quaitzite. Some 
manganiferous quartzites are. however, formed in this way. But in 
the rock so formed the manganese-ore is distributed in rounded patches. 
As an example attention may be drawn to the photo-miciograph of such 
a rock from Sivarajpur in the Panch Mahals. Bomb;^y, shown in fig. 1 
oi Plate 10. Other localities for the black quartzites are Kodegaon, 
