Open Hole Core Clock approximately 4" in diameter from the Clear Fork formation located 4,900 feet below the surface. This rock is estimated at being 230 million years old. This Clock is a great display of the core sample formation that sets on your desktop or book shelve as a beautiful displayof the rock formation below. The Clock you purchase will be a beautiful display in color and rock type of the Permian Basin oil field Clear Fork Formation. Each core sample is unique, a one of a kind and the one you purchase will be taken from our current stock of clock samples