Union College Geology Department, Physical Geology, sedimentary rocks page Sedimentary Rocks Illustrations and explanations to accompany the sedimentary rock lab. Some shales are very soft and fall apart in water, others can be quite hard. Shale is the most common sedimentary rock type on earth.
Grains are too small to identify except as indicated by dark or light color.
The grains in this sample are moderately well rounded and well sorted. Grains in arkose are usually angular, indicating a short transport distance from the source area. This sample happens to bee poorly sorted, though this is not a characteristic of most arkoses. Clasts may be any rock type, and are commonly a mixture in any one outcrop. Notice the single crystal crinoid stem fragment in the bottom left of the enlargement.