Stone mined with silk touch pickaxe is not the same as stone created by a furnace

Stone blocks that are mined with a silk touch pickaxe cannot be stacked with stone blocks that are smelted in a furnace (but placed blocks from the furnace can be mined with a silk touch pickaxe to get the same block as naturally generated stone). Only stone blocks that have been mined with a silk touch pickaxe can be traded with stone masons.