Jack @jkallmeyer – Thanks so much for the detailed explanation and information. I am writing a short article for the Friends newsletter on the brachiopod geodes, and will add this information with credit. I would also like to include the photo that you posted, if that is ok. That is a spectacular example! Thanks to Victor and Bill for the input, as well. I, too, thought that the outer crystals were probably quartz, so I really learned a lot from the forum thread. Thanks myFOSSIL community!