I found this beautiful euhedral pyroxene crystal in thin section today. There is one thing that I can´t explain though.
In crossed polarizers, the crystal shows two different interference colors, which do not change as I rotate the table (no color shifting, no extinction).
As far as I know, this happens only in basal sections. But then why are there two different interference colors ? Could it be pyroxene twinning ?
Thanks for all your answers.