I'm interested in knowing what features can still be discerned.
I've been struggling find any image of a thin section of a rock under a regular light microscope, or a petrographic microscope with the polarizer and analyzer removed.
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It would look almost identical to the image obtained using plane-polarised light.
Some minerals would look darker, especially those with strong pleochroism such as biotites and amphiboles, because all light is now transmitted or blocked regardless of orientation. Minerals with large relief differences such as carbonates (e.g. calcite) would cease to have the differences and would just have high relief.
From a static image it could actually be hard to tell that there is no polariser. A careful and experienced observer might deduce it from small hints, given some prior knowledge on what the rock contains.