In article <3997786E.B6B66551@yahoo.com>, Adam <bel### [at] yahoocom> 
wrote:

> Wait, of course Iceland spar, that is, calcite, exhibits 
> birefringence. I don't know what I was thinking with the dihydrate of 
> calcium sulfate, I mean gypsum. I didn't even mean gypsum when I said 
> it.

I don't think crystalline calcium carbonate is the only mineral to 
exhibit this behavior, though...I just can't think of another.


> Gypsum is what causes noncarbonate hardness of water.

I didn't think calcium sulfate was soluble enough to really affect water 
hardness.


> Come to think of it, how would I do double refraction anyway?

By averaging the results of calculating refraction twice, with different 
iors?

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
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