Stratus (St) Found at very low levels (less than 2000 meters, or 6500 feet), stratus clouds are thick, large, heavy-looking gray clouds that dominate the sky. Precipitation normally does not occur with this cloud, although drizzle or mist may be observed.
Shale is a fine-grained sedimentary rock which is formed by the compaction of silt and clay-size mineral particles. Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism.
Refer to Metamorphic Rock Photos for more visual examples of each of these metamorphic rock types. Foliated (Layered) Metamorphic Rocks 1. slate Slate is metamorphosed shale. Slate is tougher than shale and it breaks into thin, flat layers. Slate is usually dark gray, but it can also be red colored.