Ilium is a rare mineral that falls from the sky. In any given year very little ilium actually falls, but it has been falling for a very long time indeed. It is primarily found in three places; deep underground, under the sea and occasionally in craters - the latter very rarely indeed. One of the most valuable pieces of jewellery one can own is a ring of ilium - indeed, it is often measured in terms of the amount required to make a ring.
