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erionite
Erionite is a naturally occurring fibrous mineral that belongs to a group of minerals called zeolites. It usually is found in volcanic ash that has been altered by weathering and ground water. Erionite forms brittle, wool-like fibrous masses in the hollows of rock formations and has an internal molecular structure similar to chabazite. Some properties of erionite are similar to the properties of asbestos; however, erionite is not currently regulated by the U.S. Environmental Protection Agency as one of the six asbestos fibers. Erionite was first described by A.S. Eakle in 1898, as white woolly fibrous masses in cavities in rhyolite lava near Durkee, Oregon. It was originally thought to be another relatively rare zeolite named offretite, which is very similar to erionite in appearance and chemical composition.
==Properties==
The chemical composition of erionite is approximately represented by the formula (Na2,K2,Ca)2Al4Si14O36·15H2O. It can be differentiated into Erionite-Na, Erionite-K, and Erionite-Ca forms based on the most dominant component. Erionite has a hexagonal, cage-like structure composed of a framework of linked tetrahedra. It consists of white prismatic crystals in radiating groups of crystal fiber. Erionite absorbs up to 20% of its weight in water, has a specific gravity of 2.02 to 2.13, and has gas absorption, ion exchange, and catalytic properties that are highly selective and depend on the molecular size of the absorbed compounds. Zeolites, in general, have good thermal stability, rehydration kinetics, and water vapor adsorption capacity.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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