Some rocks according to their use or texture are classified into different types. Know more about Lignite Texture and Diatomite Texture. Types of Lignite are Xyloid Lignite or Fossil Wood and Compact Lignite or Perfect Lignite whereas the types of Diatomite 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. Lignite and Diatomite were used for creating 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. Lignite and Diatomite were used for creating petroglyphs.