Niobium sheet scrap.
The maker of the above coin from Viinamarisaar included this nice little bit of niobium sheet to show the type of material his coins are stamped out of. Source:eBay seller b-turner Contributor:eBay seller b-turner Acquired:24 February, 2007 Text Updated:24 February, 2007 Price: Donated Size: 0.5" Purity: >99%