The Willamette Meteorite weighs 15.5 tons. This iron meteorite, which was found in Oregon, is the largest ever found in the United States and the sixth-largest in the world. The smooth surface melted during its blazing entry into the atmosphere, while the pits formed on the Earth's surface.
Iron meteorites form when large enough asteroids have had molten interiors catastrophically collide with other asteroids. These huge collisions blast out material from the molten iron core of the asteroid on orbits that reach Earth after millions of years.