in <3A528654.CD0AB098@online.no> Tor Olav Kristensen wrote:
>
>Very clear illustrations of the phenomena,
>but what is a 1/4 lambda plate ?
>

A quarter wave plate is made out of a birefringed material (thin plates of 
mica). A birefringed material makes light of orthogonal polarizations 
traverse the material at different velocities. One wavefront will be ahead 
of the other by a distance that depends on the thicknes of the material. 

wave plate.
It is for example used to determine wether you have circular polarized 
light or a combination of linear- and  non-polarized light.


>I didn't know that minerals had these properties as well.
>Did you use some kind of (semi-)transparent minerals ?
>Do you know of any "everyday" mineral materials that I 
>could use for experimenting ?
>And what are "schliffs" ?

To start with the latter, "schliffs" are higly polished and very thin 
slices of stone/mineral. If you make them thin enough you can look throug 
every stone. In for example a granite there are several minerals, each 
with its own optical properties. In polarized light each will show in a 
different colour and density.

Attatched a micrograph of Asperine in polarized light. Cant find the 
colour print :(

Ingo

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