Magnetic Balls
A few years back these were a real hit at Christmas time. I bought three sets of 216 balls each (they came in a cube with 63 balls). One set was colored but the coloring has mostly come off them all and they are plain steel colored balls now. They are not steel, however, being made of neodymium. You will find neodymium on the periodic table of elements with the symbol Nd and atomic number 60. It is one of the lanthanide elements, often referred to as rare earth metals, although neodymium isn’t actually particularly rare. The magnets are actually an alloy of neodymium, iron, and boron (Nd2Fe14B). Shortly after I bought them for Christmas, they were taken off the market because they are dangerous if swallowed, particularly if two are swallowed separately. If two stick together with a fold of intestine between them, it can be very serious (seriously bad).