I have just made a new version of my guide. Now you can find every floor connected with tinted/marked rock that you can meet at this specific level. On every floor except Womb and Utero you can find 2 kinds of these rocks (Womb and Utero have only one). First of them is rock very similar to already existed, but has a small x-mark and its a little bit tinted. Second of them it's an unique rock with the same shape on every floor with different colour version (again except Womb and Utero) and it doesn't have "brother" without x-mark. I have taken images from grapics.a file from steam folder so you can be sure that everything is correct. Have fun :)

Here is a photo which contains every tinted/marked rock in the game. Actually, unlike previous Binding of Isaac game, some of them are really hard to notice: