Neodymium belongs to the rare earth metals and is a special material: In combination with iron and boron (Nd2Fe14B) it can be used to produce the currently strongest permanent magnets in the world.
The majority of NdFeB magnets are produced in China today. The reason for this is that one of the raw materials, neodymium, is 97 % degraded and extracted in China.
The lacks have a Nickel-copper-nickel coating. This gives you an attractive, silver surface.
Here available as 8 Pack with many different depths.