Chaos Iron appears to initial inspection to be lead in both color and weight. It often in some lumpy mass, as if it was melted
However, this metal hails from the Everchanging Chaos of Limbo. So, upon a second inspection, that lump of metal will often be seen to have grown spikes, or started to express even stranger shapes. The very inspection of chaos iron is what causes it to change shape, at least that is what the sages believe.
As for uses, chaos iron is mostly useless. Attempting to shape for armor or weapons ends up being a process of futility.
A lump of the metal can be affixed to chain or rod to make a mace or flail. These weapons are +1 magic weapons as result. However, if the wielder rolls a natural 1 on an attack roll, the weapon has transformed instead into some strange unwieldly mass. The weapon will have disadvantage on further attacks.
Legends tell of a smithing method to treat chaos iron to avoid this issue, and to take advantage of the mutability of the metal.