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Posted by: Donald Kasper
You don't know what you have until you have a method of spectroscopy to scan it. Otherwise, you are guessing. Send me a sample, and I will scan it. All sedimentary sites with agate and cherty agate is overlain by bentonite. You just have to look. For older rocks, the looking is harder. It took longer to find the bentonite in the Kentucky agate geology, for example. But, armed with a detailed master key I worked out for 4300 cm-1 infrared clay minerals, I can see the clays despite their trace occurrence in silica rocks. it is the same spectral region used in planetary remote sensing and works for very specific physical reasons.