Some rocks according to their use or texture are classified into different types. Know more about Skarn Texture and Shale Texture. Types of Skarn are Endoskarns whereas the types of Shale are Red Shale, Black Shale, Green Shale, Grey Shale and Yellow Shale.During historic times, some rocks depending on their hardness were used to create Pictographs and Petroglyphs. Rocks which are hard were generally not used. Pictographs are paintings or drawings that have been placed or created on the surface of rock. Skarn was not used to create pictographs whereas Shale is used to create pictographs. Petroglyph is an image which is carved into a rock. These are images created by removing part of a rock surface by incising, picking, carving or abrading, as a form of rock art. Skarn was not used to create petroglyphs whereas Shale was used to create petroglyphs.