Hmm... interesting point. Usually items in the tool slot don't grant intrinsics... so I either should remove the intrinsics from the stone heart, make an exception for the stone heart or allow that for all items.

I don't like any of these options right now :-/ *Sigh*

The cornucopia and horn or plenty have the same issue. They are tool items that are supposed to grant intrinsics, but it's not actually possible to get them due to the intrinsics not being granted in the tool slot (or anywhere else).

EDIT: My vote would be for tool-type items (and only tool-type items) to grant their intrinsics when equipped in the tool slot. This would be in line with the other item slots, including the similarly-nebulous missile slot.

Fixed as suggested by Grond.

I’m curious if this means that the artifact pick-axes also apply bonuses in the tool slot.

Sadly, picks count as one handed weapons, so you have to wield them to get the bonuses.