In Binding of Isaac, the earlier levels have blue rocks that when bombed yield usable items and/or chests. In the womb, the rocks are red and I haven't seen any that stand out from the rest. Is there a blue rock equivalent in the Womb that when bombed will give the player items?
The X rocks do exist in the womb. The trouble is they look identical to all other rocks, there is no x to define them, or even a different shade of colour. The only way to tell that you even found one is by watching the items pop out of it when it's destroyed.
You're not going to find them reliably, and unless you have more bombs than you can count (like from getting the skeleton key and then the Bombs are keys pill), you're not exactly going to blow up every rock in the room.
In the womb, you're most often going to find the rocks by accident, when trying to damage an enemy, or get to some other treasure that's blocked off by rocks.
These are actually called X rocks. They're in the Womb too, but harder to notice. You're looknig for the darker tone and the X-marks-the-spot mark.
Normal ones look like this (from the wiki):
The womb ones look different obviously...can't find any pictures though, has anyone else? People on the Wiki have expressed their difficulty finding them and I've never found/noticed one myself.