alunite

[al-yuh-nahyt]
noun
a mineral, a hydrous sulfate of potassium and aluminum, KAl 3 (SO 4 ) 2 (OH) 6 , commonly occurring in fine-grained masses.
Also called alumstone [al-uhm-stohn] .


Origin:
1865–70; < French alun (< Latin alūmen alum1) + -ite1

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alunite (ˈæljʊˌnaɪt)
 
n
a white, grey, or reddish mineral consisting of hydrated aluminium sulphate. It occurs in volcanic igneous rocks and is a source of potassium and aluminium compounds. Formula: KAl3(SO4)2(OH)6
 
[C19: from French alun alum (from Latin alūmen) + -ite1]

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Encyclopedia Britannica
Encyclopedia

alunite

a widespread rock-forming sulfate mineral that occupies pockets or seams in volcanic rocks such as rhyolites, trachytes, and andesites, where it presumably formed through their chemical reaction with escaping sulfurous vapours. It has been used as a source of potash (during World War I) and as a source of alumina (during World War II); in Europe it was once used extensively to make potash alum, and it has been mined for this purpose since the 15th century. Large deposits exist near Beregovo, Ukraine; Almeria, Spain; and Bullah Delah in New South Wales, Australia. For chemical formula and physical properties, see sulfate mineral (table)

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
These hills are the site of major deposits of volcanogenic uranium and replacement alunite.
Further evidence for this is the presence of a mineral in the plume called alunite.
Intense alteration reduces host rock to alunite and clay.
Field examination showed the kaolinite and alunite may be in hydrothermally brecciated rock.
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