Red can indicate iron if we are dealing with iron ore but since iron ore is pretty hard to find and there are tons of other chemicals which make red, I normally do not expect to find iron in enough quantities to bother me. Red River along Texas-Ok border or red clay of Georgia for instance?
But the rock type is likely to be a combo of various types from what I see. First there looks like layers of sediment and then that sedimentary rock looked like it was remelted and moved and shaped making it Igneous. So many ways to form rocks but one of the more common types is conglomerate meaning it is a combo of several other types.
So you may just have a conglomeration of rocks in the sink, none of which are hazardous! If you have good hard water with lots of buffering (GH/ KH) you are not likely to see any change when adding a few minerals from rocks which degrade really slowly. If you have soft acidic water, it takes more watching as you have no buffers to resist change.
Just looked at your location and might want to change the idea of iron, depending where they were collected. If from SE of you, in Rolla area or SE, there is a better chance of iron there. Still would not worry me much if the snails are happy.
Last edited by PlantedRich; 04-15-2020 at 02:42 PM.