This is a fossil Hickory leaf (Carya antiquorum) from the Fort Union Formation of Montana. The color of the rock and the leaves is rather unusual, and different than most of the leaves seen from the Fort Union Formation. They were collected from a locality where a fire in a nearby coal seem "cooked" the rock at sometime in the past. This changed the color and gave it a chalky texture.
There are some areas of restoration on the surface of the leaf, where there was some flaking onto the negative.