Why is Natrolite useful in testing cross hairs?

Are you sure you don't mean crossed polarizers?

there are two things that natrolite and metanatrolite zeolites display under cross or convergent nichols.
Think extinction and optical figure.

It's not me that posted the question.

I know, I'm just lazy at going back up to the penultimate poster. I wish no offense. Hey, I've just shot my wad explaining why my spelling has improved, SO allow me one failing .K?

I'll allow you as many as you need. I'm not here to break your balls.