I flushed out my well water filter recently and photographed more of those "tiny doughnuts" shown in my previous post. The larger ones are about pin head size. Found two white flakes (in one picture) that seem to have some kind of surface structure, and in another is a brown slender object that looks like a very small fossilized bone or plant part. To the naked eye what I have looks like a small pile of beach sand, but my well is in Middle Tennessee several hundred miles from the nearest beach, the Gulf of Mexico.