Chemical Composition of ObsidianĬhemical composition of it is close to these rock rhyolite and granite. Another common black type is snowflake obsidian, having inclusions of small white crystals. Sheen obsidian has golden effects, while rainbow obsidian possesses characteristic rainbow luster. Volcanic glasses also differ in terms of their structure and texture.Īir bubbles that are imparted in the course of magma flow, are aligned in a regular pattern in some types. Not have their own classification, but they can be characterized using the TASĭiagram in terms of their chemical composition. Volcanic rocks containing more than 80 vol. 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.
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