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According to some of the old data (which may be accurate, or not) the particle size varies: from 0.010mm to0.325mm, so 0.02mm is seen as a theoretical average size only. Actual specimens may be...

It certainly has the thick and thin layered banding that you associate with these stones, and the colour is about right. They seem to be greyish/yellow/tan most often with orange/brown splotches and...