Chap. MI. ] 
PIEDMONTITE. 
191 
pyramids. The mineral, when not crystalline, usually occurs as dis- 
seminated grains, especially in the cr}-stalline limestones and the 
gneisses associated therewith, and as nodules, also in the crystalline 
limestones. In these limestones the piedmontite nodules are usually 
associated with nodules of manganese-ore, and sometimes a nodule of 
manganese-ore is bordered with a thin rim of piedmontite. as in Plate 
14. The origin of these limestones and gneisses is discussed on 
pages 298 — 302. In the phyllite of Kajlidongri the mineral occurs in 
the form of small prisms. 
In colour the mineral varies from black, as in the crystals of Jothvad, 
to dark reddish-black and deep crimson, the latter colour being best 
seen in the piedmontite nodules found at Ghogara. In these nodules, 
which are often as much as 3 inches long, the piedmontite is sometimes 
in parallel fibres, so that the mineral has then some resemblance to 
crimson sUk. In the first of the Kajlidongri rocks the mineral may be 
described as being of a pansy-purple colour. 
The colour imder the microscope is very striking, consisting of various 
shades of yellow, orange, red, pink, amethyst, magenta, carmine, and 
even blood-red, the latter being an exceptional colour. Some of these 
colours are, of course, not true axis colours, the colour seen in any 
random section under the microscope being usually compounded of all 
three axis colours in varying proportions. In a few cases I have worked 
out the pleochroism scheme. These are given below : — 
a to r 
Ghogara Canary yellow Salmon to pale pink Amethyst to carmine or rose. 
Mohugaon Patchy yellow and Burnt sienna to clove- Amethyst to carmine. 
orang?. brown. 
Jothvad No. 1 Deep orange-red Very deep red \rith ame- Deep amethystine or crimson 
thyst tinge. lake. 
Jothvad Xo. 2 Orange to orange- Magenta or deep ame- Brownish lUac to reddish 
scarlet. thystine. chestnut. 
Kajlidongri Xo.l Orange to brown- Vioiet-rose with a brown- Magenta to rose. 
ish orange. ish tinge. 
The above determinations should be regarded as provisional only and 
liable to modification when the Indian piedmontites are more carefully 
examined. The other characters noticeable under the microscope 
are the high index of refraction, and the very high double refraction, 
although this is difl&cult to observe, except in extremely thin sections, 
ouing to the strong colouration of the mineral. Further the mineral 
is often twinned. 
