Rockhounding Polariscope

In gemology polariscopes are used mainly to determine whether gems are singly or doubly refractive. They are also used to determine optic character.

Basically they are largely used to distinguish between singly-refractive stones like red garnets and spinels and doubly-refractive gems like red ruby and other corundums as an example. (There are many double-refractive gems but fewer single that are cut as gems). The former transmit the same color in all orientations while the latter splits light into two  or three directions (dichroismm or pleochroism) with the result tha different colors are visible when the gem is viewed in different orientations.

While useful in gem ID that determination is also critical for gem cutters and rough
buyers. In cutting corundums (ruby and sapphire, for instance) the best color must be oriented so it shows through the top (crown) of the stone.

It's a lot more involved than that but it's late and I'm off to bed.

Interesting ideas.