I have this one and it’s worked really well. Keeps flavor. It looks gray , but after you season it and use it a few times it turns black/dark gray. And it’s stays that way. I use a tooth brush with water (no soap) when I clean it.

Spicy Bay Foods - Volcanic Rock Molcajete

Don’t buy anything from China, if you want to be on the safe side. You don’t want concrete. Not granite either. You want Volcanic rock. That’s what retains flavor.

This is what mine looks like completely dry after a few uses