This is a beautiful example of fossilized nautiloids with calcite (aragonite?) crystals in matrix rock. It comes from a Cretaceous period deposit (approx. 79 to 149 million years ago). This specimen comes from the Bear Paw Formation in Montana. This block has been partially prepared to reveal some of the nautiloids. More detail could be revealed with further preparation.
Refer to the photos. The brass centimeter cube is shown for scale and is not included. You are purchasing the specimen shown. It weighs approx. 1.25kg (or 2.75 pounds), and it measures approx. 5 by 5 by 3.5 inches in size. Your purchase will include an ID label.