Basalt from the Pleistocene of Arizona, USA. (~9.7 centimeters across at its widest)

This is a weathered, slightly vesicular basalt from a cinder cone volcano in Arizona. Cinder cones are relatively small, steep-sided cones of loose igneous debris. They have few eruptions and a relatively large summit crater. Cinder cones are principally composed of scoria and vesicular basalt.

The cinder cone volcano from which this specimen derives is known as Vulcan's Throne, which is about 73,000 years old. Lava flows from the volcano flowed into the Grand Canyon itself and blocked the Colorado River, forming a long lake. Water levels eventually overtopped the lava dam, creating a large waterfall. Erosion destroyed the lava dam and the lake drained. This sequence of events occurred at least 13 times in the history of the Grand Canyon.