Types of Coal and Obsidian
Some rocks according to their use or texture are classified into different types. Know more about Coal Texture and Obsidian Texture. Types of Coal are Peat, Lignite, Sub-Bituminous Coal, Bituminous Coal, Anthracite, Graphite whereas the types of Obsidian are Fireworks Obsidian, Mahogany, Sheen Obsidian, Snowflake obsidian and Velvet Peacock Obsidian.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. Coal was not used to create pictographs whereas Obsidian 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. Coal was not used to create petroglyphs whereas Obsidian was used to create petroglyphs.