Shale creek bed

Fine-grained, dark grey to black, dull luster, earthy smell when wet, fissile (splits into thin layers). The individual grains are too small to be seen with the naked eye. Mohs hardness typically 2.5-4.

Formed from the compaction of clay, silt, and mud particles in low-energy environments like river deltas, floodplains, and deep ocean basins. Typically formed over millions of years, often from the Paleozoic to Cenozoic eras, but can vary greatly depending on the specific deposit.

Historically used as a source of kerosene (oil shale), and for brick and cement manufacturing. Specific types can be a source of natural gas (shale gas) and petroleum. Also used as road fill and aggregate.

Shale is the most abundant sedimentary rock, accounting for over 70% of all sedimentary rocks. It often contains fossils of ancient marine life, making it valuable for paleontological studies. The fissility (tendency to split) is due to the alignment of clay minerals perpendicular to the direction of compaction.

In the field, shale is identifiable by its dark, often grey to black color, very fine grain size, and its characteristic splitting into thin, platy layers (fissility), especially when exposed to weathering. When wet, it often has a distinctive earthy or 'muddy' smell. It is commonly found in sedimentary basins worldwide. In the context of the image, the exposed bedrock in the creek bed appears to be fractured shale, creating a rough, layered surface. Collecting tips: Look for fossils between the layers, especially in unweathered specimens.