Some rocks according to their use or texture are classified into different types. Know more about Trondhjemite Texture and Slate Texture. The types of Trondhjemite and Slate are Not Available.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. Trondhjemite was not used to create pictographs whereas Slate 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. Trondhjemite was not used to create petroglyphs whereas Slate was used to create petroglyphs.