2h. Clinker Formation

North Dakota is full of brick-like masses of baked and fused clay, shale, and sandstone that color and shape the landscape. These baked materials, known as clinker (or locally as “scoria”), formed in areas where seams of lignite coal burned in prairie fires or lightning strikes. This produced heat that baked the nearby sediments to a form of natural brick.

Clinker looks like scoria, but that’s technically inaccurate. Clinker is a sedimentary rock and scoria is volcanic.