Chap. VI.] 
SPESSARTITE. 
177 
This variation in the colour of spessartite, both in the hand-specimen 
and under the microscope, is very interesting, as it points to a great 
variation in the composition of the mineral. It would be very interest- 
ing to analyse a series of specimens of this mineral to find out what is 
the connection between the colour and composition. It would probably 
be found that the main factors in producing this variation in colour are 
the relative amounts of manganese and iron. It is further interesting 
to note that not only does the colour of this mineral vary from one 
^ . crystal to another, but that often there is a great 
ooui zoning. variation between the colour of the outer and inner 
zones of the same crystal. I have not actually noticed this macro- 
scopically, but it is a common phenomenon under the microscope. Thus 
the pink example from Bichua referred to above is nearly colourless m 
the centre ; whilst in a specimen of gondite from Kodegaon, the garnets 
are sometimes sulphur-yellow throughout, and some times colourless in 
the centre and yellow on the outside, this latter phenomenon being very 
frequently observed. In an example from Jothvad the mineral is yel- 
low and light brown in patches, tending to be yellow towards the centre. 
Another cause of variation in the colour of spessartite is inclusions. 
The normal colour of a piece of typical gondite, i.e., the fine-grained 
rock composed of spessartite and quartz, is a fairly light colour, especially 
some shade of yellow, cinnamon, or grey. But sometimes the rock shows 
purplish or reddish tints, as in cases from Hatora and Ukua. Under the 
microscope this coloiu- is found to be due to the presence in the centre 
of each garnet grain of a cloud of very finely divided red dust, which is 
probably ferric oxide or hematite. Such rocks are often banded, some 
^ ■ layers being reddish or purplish due to the presence 
of these inclusions, and some of them of the 
normal light colour of gondite, the garnets in such layers being found 
under the microscope to be free from the inclusions found in the 
other bands. In some of the Chargaon garnets definite inclusions of 
red hematite are seen under the microscope, as well as brown films, 
perhaps of limonite ; the hematite inclusions were probably formed at 
the same time as the garnet, and probably express the fact that there 
was a small surplus of ferric oxide over that required for the formation 
of the garnet. The limonite films, on the other hand, occupy cracks, and, 
presumably, were introduced subsequent to the formation of the garnet. 
Hematite also occurs in patches in spessartite in gondite from Kajlidongri. 
Spessartite is sometimes quite free from inclusions ; but it more often 
contains them, either of the kind noticed above, or of other kinds. 
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