Although they are not the most abundant meteorites that have been found on Earth, many people are most familiar with iron meteorites. This is largely due to the fact that even a casual observer may readily identify them as meteorites due to their metallic content and their considerable weight. Also, since they weather slowly they are often bigger than other types of meteorites. Iron meteorites are believed to have formed in deep space from supernovas or the cores of planets or asteroids. In addition to iron, these meteorites contain a certain amount of nickel, and the two metals combined are exceptionally hard, a characteristic that appears to greatly facilitate their survival in deep space.