-0.2 speed ( not applied until the next time Isaac's speed stat is updated or upon taking damage).
-0.2 maximum speed.
+0.2 tears ( not applied until the next time Isaac's tears stat is updated or upon taking damage).
Notes
Has a small chance to be dropped from a destroyed tinted rock.
Normally only appears once per run, but can appear again if Isaac's items are re-rolled with D4, D100, or a Dice Room.
Always has a chance to spawn as long as Isaac does not currently have it. This includes the possibility of spawning and obtaining multiple copies of The Small Rock on the same floor if not picked up the first time.
Taking the rock in the Boss Rush from a tinted rock in the room will count as taking an item and consequently trigger Boss Rush. The other items do not disappear and will stay until one is picked up.
Interactions
Diplopia/Crooked Penny: Additional copies grant an additional tears up and speed down with no further increase in damage.
In the original Binding of Isaac, the player's tears would take on a grey color after Small Rock has been picked up. In Rebirth, however, the tears will be red.
However, before the Halloween Update, the player’s tears were blood tears. The reasoning for the change from blood to grey is unknown.
Head Trauma is unlocked by default, despite the fact that Small Rock isn't. This item, TMTRAINER, Dirty Mind and Spirit Sword are the only items that appear in challenges before they are unlocked. Small Rock and TMTRAINER are also notable for not being unlocked by beating the challenge they appear in.
not applied until the next time Isaac's speed stat is updated or upon taking damage).
-0.2 maximum speed.
D4, 
D100, or a 
Dice Room.
Boss Rush from a tinted rock in the room will count as taking an item and consequently trigger Boss Rush. The other items do not disappear and will stay until one is picked up.
Diplopia/
Crooked Penny: Additional copies grant an additional tears up and speed down with no further increase in damage.
TMTRAINER, 
Dirty Mind and 
Spirit Sword are the only items that appear in challenges before they are unlocked. Small Rock and TMTRAINER are also notable for not being unlocked by beating the challenge they appear in.
The Binding of Isaac: Rebirth
