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.
Slate can also contain abundant quartz and small amounts of feldspar, calcite, pyrite, hematite and other minerals. Most slates are gray in color and range in a continuum of shades from light to dark gray. Slate also occurs in shades of green, red, black, purple and brown.n the coal mining industry of the Appalachian Basin, the word slate is still used by many miners to in reference to the shale that forms the roof and floor of a mine and for fragments of shale that are separated from the coal in preparation plants.