What instrument is indispensable for geologists to view a thin section under both PPL and XPL?

Answer

Petrographic microscope

The petrographic microscope is the indispensable instrument that allows geologists to view the sample under both plane-polarized light (PPL) and cross-polarized light (XPL) to reveal optical properties.

What instrument is indispensable for geologists to view a thin section under both PPL and XPL?
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