![]() ![]() ![]() The meaning of obsidian (Latin o bsidiānus) is said to have come from a misreading involving the word "obsiānus". Obsidian continued to be used in the ancient Middle East for thousands of years after the introduction of metals. This was primarily because its sharp edges made it ideal for blades and tools. It was widely traded by many ancient cultures. Polished black obsidian was used as a mirror by the Aztecs and Greeks. Most material comes from countries with extensive volcanic activity. Being a natural glass it's brittle so must be handled carefully. On Mohs scale of hardness obsidian grades 5 to 5.5. Spherulites tend to have a duller lustre than the host rock. The word "vitreous" is widely used to describe the surface of a stone whose surface interacts with light in a similar way to glass. These tend to be composed of quartz and feldspar. They're known to have radiating fibrous needle-like crystals. The spherulites in snowflake obsidian are difficult to see in detail without powerful magnification. The presence of iron and magnesium produces black obsidian which is the most well known. Hematite causes the red and brown varieties whilst inclusions known as spherulites (spherical bodies) cause the whitish grey markings in snowflake obsidian. Tiny bubbles caused by water vapour, air or gas can also produce different types of sheen.Ī golden sheen is known as sheen obsidian whilst iridescent material with circular-like patterns is known as rainbow obsidian. The colour of obsidian is determined by inclusions and/or impurities present. Oregon has many gem-grade varieties including mahogany, red, black, rainbow and snowflake obsidian. The problem with using obsidian for this purpose is that it's not particularly hard and is also brittle.ĭifferent types of obsidian can be found in many locations around the world. The edge of a non crystalline material is completely smooth so the incision is cleaner and more precise. ![]() They create a finer incision hence wounds heal faster with less tissue damage and scarring.Ī steel scalpel has a cutting edge similar to a saw due to the metal's crystalline structure. In recent years scalpels used in surgery have been made from obsidian blades instead of conventional steel. It was widely used during the Stone Age for knives, spear tips and arrows. Obsidian is one of the sharpest of all naturally occuring materials. ![]() This is because of its amorphous (non crystalline) structure. When obsidian breaks it has razor-sharp edges. This characteristic is typical of many brittle, non crystalline materials. The correct term for this type of break is a conchoidal fracture. The way obsidian breaks is very similar to glass. One respected geologist describes it as "a congealed liquid with impurities of rock and a limited number of microscopic crystals". The problem however is coming up with something more suitable. Most magma contains at least 70% silicon dioxide which is the main constituent of obsidian.Īlthough obsidian is often referred to as a "stone", some geologists argue that's not an accurate description. When compared to the age of many rocks and minerals that's relatively young. Obsidian is rarely older than about twenty million years. The glass that subsequently forms will often be free from dirt, ash and other impurities. This tends to occur close to the vent of the volcano. Some of the finest obsidian forms beneath the surface of Earth as magma seeps between fractures in rocks. These materials are correctly known as mineraloids. The type of magma that forms obsidian has a low gas and water content.Ī naturally occuring solid that's non crystalline is a rock not a mineral. Other varieties include pumice, apache tears, perlite and pitchstone but there are many more. The type that forms depends on the nature of the volcanic eruption, the chemical composition of the magma, the presence of gases and the speed at which the lava cools. There are many different types of volcanic glass. Sub-micron means crystals are smaller than one micron or one millionth of a metre. They may form after a few weeks but will only be "sub-micron". Lava initially cools fairly rapidly but due to insulating properties the cooling process quickly slows down.Ĭrystals have insufficient time to grow if lava cools very fast as in hours to days. Once spewed out from the vent of a volcano it becomes known as lava. Magma is molten rock from beneath Earth's surface. This burning hot material often cools so rapidly that crystals do not have time to grow. Obsidian is natural volcanic glass that forms when a specific type of magma cools and solidifies. Obsidian Meaning, Properties, Facts and Photos Contents ![]()
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