aurum

Aurum, auri, n., second declension, and entirely regular. The adjective is aureus, "golden", which doubled as the name of the standard gold coin, so aureus in a text about money is a coin and not a colour.

Material is expressed either with the bare ablative or with ex plus the ablative, both correct: auro factus and ex auro factus. English gold is Germanic and unrelated, which is why nothing in the everyday vocabulary looks like aurum; the Latin came in sideways, through aureole, oriole, the heraldic tincture "or", and the chemical symbol Au. French or and Spanish oro are the direct descendants.