Lignite is by far the most common. fossil at Dinosaur Park. Many pieces retain the shape and texture of the tree bark, twigs, and leaves from which it formed.
Lignite is a geologically young type of coal. The lignite at Dinosaur Park is 115 million years old, but most of the coal used for energy is 400 million years old. Like all coal, lignite is formed from various kinds of plants that accumulated at the bottom of a body of water. Eventually, the gradual but continuous changes in the Earth's geology buried these plants. Immense pressure over millions of years caused the water to be squeezed out of the buried plants, leaving nothing but carbon behind.