All sorts of prehistoric artifacts made from obsidian have been found by archeologists, including knives, arrow heads, spear points, and scrapers. Over time, ancient peoples learned to break obsidian into tools of various shapes. This feature is why one of the first primitive uses of obsidian was as a cutting tool. That means obsidian breaks into pieces with curved surfaces that are razor thin and extremely sharp. Geologists call the way obsidian breaks a conchoidal fracture. One of the most unique features of obsidian is how it breaks. Obsidian can also be found in Hawaii and Alaska. In the contiguous United States, you'll only find obsidian west of the Mississippi River in states such as Arizona, California, Idaho, Nevada, New Mexico, Oregon, Washington, and Wyoming. For example, significant deposits of obsidian can be found in the United States, Canada, Mexico, Guatemala, Argentina, Chile, Greece, Hungary, Italy, Iceland, Russia, New Zealand, Japan, and Kenya. Obsidian can be found all over the world in areas with volcanic activity. If trace elements are present in the rock, it might also take on rarer shades, such as red, orange, yellow, or blue. Black is the most common color of obsidian, although it can also often be found in shades of brown and green. When most people think of obsidian, they think of a deep black, glassy stone. Obsidian is usually considered an extrusive rock, because it usually solidifies above Earth's surface where the edges of a lava flow come into contact with cool air or water. Obsidian is quite unique due to its smooth, uniform volcanic glass texture. When that happens the molten magma forms an igneous rock known as obsidian. In fact, sometimes molten magma comes into contact with the air or water on Earth's surface and cools so rapidly that its atoms don't have time to form a regular crystalline structure. While many such television shows and movies about volcanoes may have many details that aren't exactly supported by science, it is true that molten magma can be cooled to form a solid. Have you ever seen a movie or television show in which a hero saves a town from sure destruction by stopping a lava flow from an exploding volcano? If so, the hero in the show may have done so by creating a cooling barrier to turn the molten magma into a solid rock.
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