Gosh there are so many different little thoughts from my trip to Nevada. Like this one I just had about the dark brown rock that is the commonest tool material on my little hill. I looked up "chert" and it is the perfect definition for this material, as far as I can tell. This is gratifying for several reasons. One is that I had almost figured out a material with nodules in some places and layers on other places, would have to be like an accreting flint but also -somehow- sedimentary. Well, what do you know, they suspect that diatomaceous layers were the source of SiO2 molecules which migrated around to form chert.
And I was trying to resolve the difference between white chalcedony [??] and brown chert. It is OK, they are compatible as different varieties of mixture between trigonal and monoclinic forms of SiO2 crystal. Don't ask me what that means.
But here is the little thought: I had decided that the brown chert and the white Chalcedony could not be the same material because the chert remains shiny when underground but the white material become crumbly like chalk. So you pull a fragment out of the ground and expect the white stuff to have deteriorated but the brown stuff to be like new (at least visually).
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