Chap. XVI. J 
GONDITE SERIES : PETKOLOGY. 
337 
It will be seen from the lists given on the preceding pages what a great 
variety of rocks there is, both constituting, and associated with, the man- 
ganese-silicate-rocks to which the name of the gondite series has been 
given. It will obviously be impossible for me to give here a full petro- 
logical account of this large number of rocks, interesting though they be^ 
and I shall content myself with giving a short account of the most impor- 
tant varieties. 
Although the number of kinds of rock enumerated above is very 
large, yet only a few of them are of frequent occurrence. These more 
frequently occurring rocks have been indicated by being printed in 
italic type in the lists given on pages 329 to 332. 
Descriptions of the more Important Rocks. 
The commonest and most characteristic member of the gondite 
series, and consequently the one to which the name 
Gondite. gondite has been given, is one made up of a 
mixture of manganese-garnet and quartz. Although 
this garnet has not the theoretical composition of spessartite, yet, if 
one can judge from two analyses (one of which was calculated from a 
rock analysis ; see page 351), it is sufficiently close to be included under 
this name. The typical variety of gondite is a fine-grained rock of 
uniform grain, the separate grains of which are just apparent to the 
unaided eye. In colour this rock varies from cream-coloured (this being 
a rare colour) through grey, yellow, buff, and cinnamon^ to reddish and 
purplish. Under the microscope it is seen to consist of very numer- 
ous small idiomorphic garnets, in some parts isolated one from the 
other and in other parts aggregated into little groups, scattered through 
a matrix of mosaic quartz, the individual grains of which are usually of 
about the same average size as the garnets. In colour the garnets are 
of some shade of yellow, varpng in thin sections from quite a strong 
sulphur-yellow to practically colourless. When the nicols are crossed, a 
very pretty effect is produced owing to the numerous uniformly-sized 
garnets appearing as dark spots scattered through a matrix of mosaic 
quartz polarizing in greys and whites. The appearance of this typical 
gondite is well shown in the photo-micrograph (Plate 1 ] , figs. 1 and 2). 
Frequently no other minerals can be detected in a thin section of 
gondite ; but just as often a careful examination of the section reveals 
the presence of a certain number of very small idiomorphic granules 
of apatite scattered through the quartz mosaic and sometimes also 
included in the spessartite. In one case, namely, that illustrated in 
II 11 
