From where I'm sitting in my home office, there is an array of glacial boulders in the flower bed outside my window. I picked them from a farmer's field (with permission) -- a wide assortment and roundish. As a geophysicist, I only know three rocks, and all three are present: granite, not-granite, and maybe-granite.
The tuff was flow-banded, and the silica followed and preserved the structure. So not exactly agate, but there are sections that look much like it. Other minerals would be cooler, but it is nice lapidary stone!
My wife caught me bashing gravel with a hammer one morning and asked what I was up to. I told her that I used to love digging for fossils and she took a note.
Maybe in elementary school... but I still have them so it likely worked. When I lived in town they started putting it in the drinking water so maybe that helped!