Neodymium - Nd
These are two samples of neodymium. One sample is a small amount of filings. The other sample is a somewhat larger piece of neodymium. The larger piece is covered by a grayish layer of oxide. The filings are much darker than the larger piece. This almost certainly also is due to a slight amount of oxidation. Neodymium is a reactive metal, which quickly tarnishes in contact with air.
Neodymium quickly tarnishes in air, and for that reason, it frequently is ampouled in a glass tube. Below, a sample of 3 grams of neodymium is shown in a little tube, filled with argon. Despite the ampouling, it still looks quite tarnished, but some of the metal still shows some of its lustre.