Aquarium Safe Rock (R4) Natural Stone Iwagumi Aquascape, Cichlid Aquarium, Terrarium Plan and Design Your Own Aquascape. Each order of Rock is Natural and Unique! Each Order contains 4 or 5 pieces of Aquarium-safe Rainbow Rock. 7 to 8 pounds; Larger/Thicker/More substantial pieces than our 8 piece selections. Organic, Natural Stone! No Plastic! No Resin! Please examine the pictures carefully! These are Natural stones and there is a lot of variation in Size, Shape and Coloration..