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 partial colony with fossils on two sides of the specimen. 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 351 grams. Your purchase will include an ID label.