Lignite coal is a low rank coal that is basically a compacted, slightly lithified peat. Lignite coals are soft, fragile, brown to black in color, and dull in luster. Many lignites are called "brown coals".
Lignites can spontaneously combust. Sometimes lightning strikes and wildfires ignite lignite coal beds Clinker beds are the burned-out remains of lignite beds. Lignite coals and clinker beds are somewhat common in parts of northeastern Wyoming, eastern Montana, and western North Dakota.
Lignite coal (4.5 cm across)