Some rocks according to their use or texture are classified into different types. Know more about Obsidian Texture and Gneiss Texture. Types of Obsidian are Fireworks Obsidian, Mahogany, Sheen Obsidian, Snowflake obsidian and Velvet Peacock Obsidian whereas the types of Gneiss are Augen Gneiss, Henderson Gneiss, Lewisian Gneiss, Archean and Proterozoic Gneiss..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. Obsidian was used to create pictographs whereas Gneiss is not 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. Obsidian was used to create petroglyphs whereas Gneiss was not used to create petroglyphs.