Chap. XII.] 
KODURITE SERIES ; MINERALOGY. 
251 
neglecting, of course, all minerals, such as manganese-ores, lithomarge, 
and chert, that have been formed by subsequent alteration. 
Quartz. — This is usually found in the most acid varieties of the series, 
and when it occurs the rock is as a rule sufl&ciently coarse-grained for 
the quartz to be about \ inch in diameter, the range for this consti- 
tuent being usually about | to | inch. The quartz is white to colourless. 
Felspar. — This is usually completely altered to lithomarge (kaolin), 
but is fairly often found forming a crumbly mass that gives a marked 
potash reaction. In rocks from Boirani in Ganjam (page 255), however, 
it is found perfectly fresh, preserved in a matrix of secondary opal (see 
fig. 2, Plate 8). It then shows under the microscope the characters 
of orthoclase. A specimen of kodurite from MamidipiUi is a friable 
granular rock in which the constituents average | to J inch across, the 
felspar being fresh though very brittle. This also gives a strong potash 
reaction, and is seen under the microscope to be untwinned. The 
evidence therefore shows that the felspar is an untwinned potash variety 
and hence probably orthoclase. It is usually allotriomorphic, but in 
the granular rock from MamidipiUi mentioned above it is sub-idiomor- 
phic, whilst in one specimen from Boirani in Ganjam there is a 
porphjTitic crystal (0"3 inch long) showing simple twiiming. 
' Apatite. — This is the most universally distributed constituent, for it 
may be found in every variety of the rocks of this series. In some cases 
it is only seen microscopically ; but it is frequently present in little 
romided bluish-green prisms from jq to | inch long, and can often he 
extracted in great abmidance from the decomposed lithomarge that 
has been formed from the felspar of the original kodurite. At Garbham, 
Ramabhadrapuram, and Devada, it is especially abimdant in this way. 
On page 1073 the find at Devada of some hundredweights of deep 
sea-green apatite in rough prisms up to 5 inches diameter is noticed, 
and it is suggested that they may have been derived from a pegmatitic 
variety of kodurite. Analysis is said to have shown this to be fluor- 
apatite. On page 1063 is described the occurrence at Kodur of a veinlet 
of lavender-coloured apatite in spandite-rock. Both this and the 
Devada crystals are mangan-fluor-apatite. 
Spandite. — In the spandite-rock this occurs in granules averaging, 
at Kodur, ^ to J inch in diameter. As the grains are all in contact 
with one another they are bovmded by flattish faces, which do not cor- 
respond to any particular directions. In kodurite the spandite is found 
both aggregated and in separate granules. These granules are usually 
II B 2 
