The rock illustrated in these images contains both clinopyroxene and orthopyroxene, and the significantly higher Cr₂O₃ content of the clinopyroxene in this sample gives it a pale green colour in plane polarized light, whereas the Cr-poor orthopyroxene is colourless (A).  A diagnostic feature of members of the pyroxene group is the {110} cleavage that intersects at approximately 90 degrees, as seen in one of the orthopyroxene grains near the centre of these images.  Orthopyroxene has maximum interference colours of upper first order, whereas clinopyroxenes range to upper second order (B).  Extinction angle can also be used to differentiate between the two pyroxenes, as orthopyroxenes have parallel extinction and clinopyroxenes have inclined extinction, though this is not well illustrated in the images here.  Sample is from a spinel websterite xenolith from the Moses Rock diatreme, Utah.  Fields of view are 5.5 mm across.  A ppl, B x-nicols.