Carborix

A tiny rock planet with a thin, reducing atmosphere, Carborix was remotely mined for millennia, first for rarer platinum-group metals and radioactives, then catalysts and semi-conductors, and eventually structural materials like titanium, iron, and nickel. Recovery operations were grinding to a half just before the Reapers hit the planet. The attack turned orbital stations and the turians' early-warning satellites into molten metal.