![]() ![]() Different regions around the world produce unique varieties of obsidian, each with its own characteristics. Geographical Origin: Obsidian can also be classified based on its geological source.Inclusions: Obsidian can also be classified based on the types of inclusions it contains:. ![]() Color Variations: Obsidian can be classified based on its color.Reason, the obsidian is sometimes regarded as a mineraloid. Structural ordering similar to crystals only in very short distances. Major minerals: Amorphous volcanic glass that exhibits the The translation into English of Natural History written by Pliny the Elder of Rome shows a few sentences on the subject of a volcanic glass called obsidian (lapis obsidianus), discovered in Ethiopia by Obsidius It is ascribed to Theophrastus who used it for the first time in 320 BC. Name origin: The name obsidian is very old. It is fragile, tough and it disintegrates to very sharp slivers. Diffusion in the very viscous acid and felsic lavas with highly polymerized SiO2 tetrahedrons is slow, thus inhibiting the nucleation of crystals and supporting the origin of the glassy structure. Obsidian most frequently originates by a rapid coooling of a felsic viscous lava. Those are combination of black and brown colours. Hand-specimen rock is common combination of two colours. Colour is controlled factor by trace element content and the character of inclusion. Also It occur red, brown-green, green, yellow and rare transparent colourless. It usually colours dark, black, grey-black to grey. Result of this formed, glass occupies more than 80 % and that have seeming conchoidal fracture and vitreous luster. It is occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes. Delete "ALLCAPS" from address before sending.Obsidian is an extrusive igneous rock. Go back to Igneous Rocks page Return to HomeÄ®-mail C.E.Jones with comments or corrections. The piece on the right has not been worked. The point on the left was made by an anthropology major at Stanford University. Native peoples around the world learned to take advantage of the way obsidian chips to make arrow heads, spear points, and other tools requiring very sharp edges. This close-up of the banded piece of obsidian clearly shows the conchoidal fracture surfaces and the glassy nature of this rock. Its dark color comes from microscopic magnetite grains. However, it also occurs with red banding and with white patches (snowflake obsidian). Note the curved, conchoidal fracture surfaces. Here are three different types of a glassy volcanic rock called obsidian. Thus, the rate of cooling of a felsic and mafic lava flow could be the same, but the felsic flow would form a glass because it is packed with silica. The high silica (SiO 2) concentrations found in felsic rocks (rhyolite composition) causes a rock to form a glass much more readily than it would in low silica rocks such as basalt. However, composition is also vitally important. Superficially, a glassy texture suggests cooling that was so extremely fast that no crystals could form. Glassy Textures If a rock looks like a block of (colored) glass, with no visible mineral crystals, it has a glassy texture.
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