This is a "Petosky Stone", which is a common name for a type of fossilized coral colony. Some types of this stone are polished and used in jewelry-making. This stone is a complete colony with fossils on three sides of the specimen and the backside is rough where it attached to the host rock while living. It is a Hexogonia species and was collected from an unknown locality.
Refer to the photos. The black centimeter cube is shown for scale and is not included. You are purchasing the specimen shown. It weighs 223 grams. Your purchase will include an ID label.