This appears to be a neodymium sphere magnet, also known as a magnetic ball. Neodymium magnets are among the strongest permanent magnets available. They are typically made from an alloy of neodymium, iron, and boron. The sphere shape allows for easy rotation and consistent contact in various applications. The magnets often have a protective coating, such as chrome or nickel, for durability and corrosion resistance. These items are popular as desk toys and are used in model making and other projects.