It is pleochroic and greenish in color in plane-polarized light (PPL) and it is dark yellow to greenish pink color in cross-polarized light (XPL) as it appears in the photograph. Is it Chloritoid? I also thought it could be tourmaline.
This is another photomicrograph in XPL . Is the marked yellowish CHLORITOID is correct?
This is the same photomicrograph in plane polarized light (PPL) of the above one Hope it may help in identifying...
I dont think that is chloritoid. Rather it looks like green tourmaline?
chloritoid has oblique extinction (~20º) and tourmaline has parallel extinction. According to this, by the disposition of your photomicrographs, its more likely to be a tourmaline
Tourmaline can be easily identified by checking its pleochroism. It gives max.obsorption in the EW direction (i.e., perpendicular to the vibration directin of polariser -unlike biotite). So please check with a biotite grain. In my opinion it is hazardous to attempt to name a mineral from a colour photograph -that too when it is associated with more than one mineral and when it is not marked / indicated on the photograph. From the photograph the rock appears to be a mica schist and the central relatively high relief tabular mineral could be tourmaline. You have not mentioned about the RI (relief) of the mineral which is the most important property of a mineral to identify in thin section -and unfortunately quite often people over look this aspect. KNRAO
Agree, just rotate the table about 45 deg in both directions and see what happens.
It is tourmaline. For chloritoid the birefringence is to high and pleochroism is inverse. Good you have kyanite in the thin section - chloritoid looks very much the same, except the greenish, rarely blue and not so intense colour, lower birefringence and frequent twins.
moreover, these minerals have high optical relief (tourmaline has signifcantly higher relief than Cld), so this seems to be tourmaline.
From above discussion It seems more likely to be a tourmaline rather a chloritoid
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