Tiffany Bogus asks: "What exactly is diamond dust and has Knoxville ever seen this?"
Diamond dust is a cloud made up of tiny crystals that forms near the ground. You can see it when the skies are clear, and because of that it's sometimes called "clear-sky precipitation."
As for seeing diamond dust here in Knoxville, we've never seen it as far as we know.
It typically requires very, very cold temperatures, and is most commonly seen in Antarctica and the Arctic.