Commentary for Avodah Zarah 91:21

Objects that have been worshipped as idols may not be offered on the altar. So there are two parts to the question of whether these rocks can be used to make the altar. 1) Does this rule apply to things attached to the ground, like rocks that are part of a mountain? 2) Does this rule apply to the things needed to offer sacrifices, like the altar, or just to sacrifices themselves?