Well the "segments" are composed from carbonate, probably calcite. Here is a picture under crossed nicols.

André Klicpera, yes, it is a mechanical defect. Not too long ago I've checked it under SEM, there's clearly visible fracturing and displacement of calcite. Since I'm still a junior geologist, it was hard to identify what it it (that's why I've posted these pictures). Still, thank you for your reply. You too, Jahn Hornung.