I just read an article, and there's a photograph of minerals near the end of it all. The caption describes it as "The photo was taken with partly crossed polarizing filters; the width of the entire field is 1.62 mm."
Would that be two CPL or two linear polarizers? And how exactly does that work, when cross polarization so often blocks a great deal more light, or can even block light completely (at a perfect 90 degree cross)?
The image:
The article:
Global Volcanism Program | Dabbahu | Monthly Reports