One of the more interesting rock formations I sell in my shop is stromatolite, aka algae jasper. A very popular source is the Mary Ellen mine, now underwater. This past summer a customer took photos of the mine pit and and sent them to me. I told him what I knew, that my family signed waivers to collect specimens so many years ago. He happens to have the same surname as our MN U.S. senator and there IS a family connection.