A material found in the bones of some dragons, made from the metals that plate them and the naturally ossified bones, Draconite is often an almost milky grey colour, with streaks of rust red. This is not always the case, and indeed Draconite can vary from wholly rusty-red and metallic, to a softly shimmering milky grey, sometimes even within the same dragon. Not all dragon bones produce Draconite, but many do, and it is a surprisingly useful mineral, both in alchemy and in enchanting, where it can often provide a great deal of extra magic to a process or bolster a set of shields or wards.
Most usually Draconite contains high levels of iron, but it does, on occasion, contain threads of gold instead (this is especially common with Glimmering Misfortune Dragons) and may even contain small quantities of silver. Indeed, Goblins claim that silver-bearing Draconite is carefully processed in order to obtain the highest quality metal used in goblin silversmithing, and that those pieces of Draconite left over are used in the defensive spells around Goblin-guarded vaults. Indeed, while it has not been proven it is believed by some that Draconite silver is a key component in Winding - and other variants of - Argentivite.
(Winding Argentivite is the invention of the wonderful @amortentiafashion, and may be read more about in the links provided above and Here. I hate that I have to include this but PLEASE DO NOT DELETE THE IMAGE SOURCE OR MY CAPTION.)