Shale is a sedimentary rock made up of tiny grains of silica, clay and other minerals. Many types of rock have few physical ...

The striations show sedimentary layers; the darker the color of a layer, the higher its oil shale content. Credit: US Geological Survey What Is Oil Shale? Caption: Oil shale: The rock that burns.

A shallow sea advances and retreats several times during this period, leaving behind the layers named Kaibab Limestone, Toroweap Formation, and Hermit Shale ... the rock reveals that its color ...