These rocks forms mostly where magma chamber is available to heat enough for mineralogical changes occurrence. These rocks have multiple features in distinguishing like schistosic, gneissic and slaty texures.
Texture is the physical character or a pattern.
Slate are formed by the metamorphism of shale. Sheets are formed in the slates where it can broke into sheets. This help in determining the slates.
Schistose is formed after metamorphism of slate where it rearrange in forming irregular sheets like character which is schistosic texture.
Gneiss is the high grade metamorphic rock of shale which is distinguished by regular interval of dark and light bands present in it. These are called gneissic bands which is the recognizable character.
Metamorphism and its changes are following
Shale- Slate- Schist - Gneiss
Shale is sedimentary rock when metamorphose produces slate and slate to schist and schist to gneiss with increasing metamorphic grades. In the same way marble is produced by the metamorphism of limestone.