Mercury has fairly a large iron core (even when compared to Earth). Mercury's composition is approximately 70% metallic and 30% silicate. The average density is 5430 kg/m³; which is somewhat less than Earth's density. The reason Mercury, although having so much iron, has a lower density than Earth is that Earth's mass is about 20 times greater, resulting in a more vastly compressed interior with a high density. The iron core fills 42% of the planetary volume (Earth's core only fills 17%).Surrounding the core is a 600 km mantle.