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[uh-loo-nuh-juh n] /əˈlu nə dʒən/
a mineral, hydrous sulfate of aluminum, Al 2 (SO 4) 3 ⋅18H 2 O, occurring as a white, fibrous crust on quarry or mine walls.
1865-70; < French alun (see alunite) + -o- + -gen Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Encyclopedia Article for alunogen

a sulfate mineral formed by sulfate solutions that attack aluminous minerals; alunogen is hydrated aluminum sulfate, formulated Al2(SO4)317H2O. It typically occurs as an efflorescence or crevice filling in pyrite-containing coal formations, shales, or slates, as well as in the gossan (weathered capping) of sulfide ore deposits and in volcanic fumarole deposits. In older literature, alunogen and other hairlike sulfate minerals were called Haarsalz ("hair salts"). For detailed physical properties, see sulfate mineral (table)

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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