Rock is any natural (non-man made) earth material. It can be biogenic (except made by man). So coal is a rock, ICE is a rock and certainly gold is a naturally occurring substance that is a mineral. Most rocks are made up of more than one mineral, although monomineralic rocks do exist. Cement is NOT a rock, plastics are not rock. I think that rock has to be substantially solid... so we do not consider water a rock nor is magma (molten rock) a rock. But when it solidifies, then indeed it is a rock. Hope this helps.