Obsidian
Obsidian is a naturally occurring volcanic glass formed from the rapid cooling of lava, primarily found in volcanic regions. Its color can vary widely, including shades of black, blue, yellow, orange, and red, depending on the chemical composition of the lava. The unique properties of obsidian include its ability to fracture in a way that produces extremely sharp edges, making it a valuable material for crafting tools and surgical instruments. Historically, ancient civilizations utilized obsidian to create arrowheads, knives, and other tools due to its sharpness and durability. In modern medicine, obsidian scalpels are favored by some surgeons for their precision and ability to create cleaner incisions with reduced scarring. Additionally, obsidian has artistic applications; it can be carved, polished, and fashioned into decorative items such as jewelry. Notable deposits of obsidian can be found in various countries, including the United States, Mexico, and Japan, contributing to its cultural and practical significance throughout history.
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Obsidian
Obsidian is a type of rock resulting from the rapid cooling of lava flows. For this reason, obsidian can only be found in volcanic areas. While obsidian is often a smoky black stone, its color is based on the chemical composition of the lava that created it. Obsidian may also be blue, yellow, orange, red, or any combination of these colors.
Obsidian fractures in a unique way, creating an extremely sharp edge. In the ancient world, obsidian was commonly used to make tools, arrowheads, spear tips, and knives. Because obsidian is much sharper than steel, it is also used as an edge for modern surgical scalpels. Many surgeons believe that incisions made with an obsidian scalpel are cleaner than those made with a steel scalpel and result in less scarring and a faster recovery.
Additionally, both ancient and modern artists used obsidian as a medium. The stone is relatively soft, making it convenient for use in both carving and sculpting. It can be shaped into beads or polished into a reflective, visually appealing form.
Background
Obsidian is a specialized type of igneous rock that forms when magma becomes trapped in Earth. Magma is a superheated, semi-liquid form of rock that is found beneath Earth’s surface. When trapped magma leaks onto the surface, it becomes lava. Lava typically flows downhill and is found near active volcanoes. If the area around a lava flow is settled by humans, it can cause property damage and loss of life, especially during a volcanic eruption.
There are two types of igneous rocks: intrusive igneous rock and extrusive igneous rock. Intrusive igneous rock occurs when magma is trapped under the surface, settling there before it rises to the surface. Over thousands or even millions of years, the magma cools while still underground. As it cools, it solidifies, becoming igneous rock. This type of rock tends to include large mineral veins and features a coarse texture.
Extrusive igneous rock forms similarly. However, while intrusive igneous rock forms beneath Earth’s surface, extrusive igneous rock forms from magma that cools after it reaches the surface. Because the surface is much cooler than the inside of Earth, magma that reaches the surface typically cools very rapidly. This traps bubbles of gas within the lava, creating rock with a unique bubbly texture. Additionally, because the rock solidifies so quickly, it looks similar to colored glass.
Overview
Obsidian forms when magma cools, so it is primarily found in volcanic areas where magma has reached Earth’s surface. It is usually considered an extrusive igneous rock because it forms on Earth’s surface. Some lava flows emerge on land, cooling upon contact with air and creating easily observable deposits of obsidian. Other lava flows are located underwater, creating oceanic obsidian deposits. Rarely, obsidian can form near the edges of a sill or dike without exposure to the surface, changing its classification to an intrusive rock. Large deposits of obsidian can be found in the United States, Peru, Japan, Italy, Kenya, Mexican, New Zealand, Russia, and Argentina.
The most common forms of obsidian are smooth, black, textured stones, the type of obsidian most commonly seen in illustrations and media. However, because the mineral deposits found in obsidian can change, it may also be red, blue, orange, yellow, or combinations of these colors. The chemical composition of obsidian is directly related to the lava that cooled to form it. Lava from different regions is composed of different minerals, which influences the tint of the stone.
The shape of obsidian depends on how the lava was flowing when it cooled. Some obsidian deposits are wide and bumpy because the lava was flowing as it cooled. If the outer shell of the lava solidifies before the inside, obsidian deposits may form large, angular blocks. Obsidian may also be found in chips, fragments, and various stages of weathering.
When obsidian is broken, it forms a unique pattern called a conchoidal fracture. These breaks are very thin and unusually sharp. For this reason, ancient peoples harvested obsidian, breaking it into small shards and then using the shards to make tools such as spear tips, arrow heads, and knives. They also appreciated the stone’s smooth, glassy surface. They used obsidian to make jewelry or polished it until it could be used as a mirror.
Obsidian is harvested to make modern tools. Obsidian-edged scalpels are extremely sharp with very thin edges. They are significantly thinner and sharper than steel blades. Many surgeons prefer to work with obsidian-edged scalpels. Because obsidian’s microscopic cutting edge is thinner and sharper than a steel edge, incisions performed with an obsidian scalpel lead to reduced recovery time and scarring.
Like ancient peoples, modern artisans use obsidian to craft jewelry. It is commonly polished to a mirrored finish and considered a semiprecious stone. Obsidian of various colors may be fashioned into beads or set in necklaces and rings. Despite the sharpness of its edge, obsidian is relatively soft. Both ancient and modern artists carved sculptures out of obsidian.
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