Yes, Mark, that is an interesting article on "Chalcedony".
He takes a good stand about when an agate is a jasper is a chert, or a chalcedony.

I could start a thread in the Cryptocrystalline section for the
Mia Zara agate from Madagascar we were looking at at John's the other day
but I am sure there will be opportunity for more and better pics later.
The Mia Zara is some of the most awesome agate I have ever seen.
It's got it all. Plumes, moss,sagenite, and fortifications, and is very fracture free.
Here's some sample pics.