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Formula: (NH4)(AlSi3)O8
Tectosilicate (framework silicate), feldspar group
Crystal System: Monoclinic
Specific gravity: 2.32 measured, 2.38 calculated
Hardness: 5½
Streak: White
Colour: Colourless
Common impurities: Mg,Ca,Ba,Na,K
Environments
Hydrothermal environments
Hot Spring deposits
Buddingtonite occurs in plagioclase altered by ammonium-bearing waters
(Webmin).
Localities
At the type locality, the Sulphur Bank mine, Clear Lake Oaks, Sulphur Creek Mining District, Lake county, California, USA,
buddingtonite occurs as a low-temperature hydrothermal replacement of
plagioclase
in andesite altered by ammonia-bearing hot springs (HOM).
Buddingtonite was the first ammonium aluminosilicate found in nature, occurring near and below the water table of
the active hot-spring system in Quaternary andesite. Typically, it
occurs as compact masses pseudomorphous after
plagioclase,
and as tiny crystals lining cavities.
In one drill hole, buddingtonite extends below the water table to depths of about 400 feet, where present
temperatures are about 100oC. In some places andesite is
almost completely replaced by buddingtonite, with only a few percent of other minerals such as
sulphur,
stibnite, pyrite,
marcasite, gypsum,
baryte, montmorillonite and
anatase
(AM 49.831-850).
A sample of buddingtonite from this locality contains admixtures of FeSr,
anatase and montmorillonite.
Montmorillonite is
capable of reversible dehydration, and its admixture explains the zeolitic
behaviour previously ascribed to buddingtonite
(AM 78.204-209).
In the sedimentary Phosphoria Formation in Idaho, Wyoming and Montana, USA, buddingtonite is associated with
muscovite variety illite, albite,
montmorillonite and kaolinite
(HOM).
In the Cedar mountains, Nevada, USA, buddingtonite occurs in metasomatised
rhyolytic
ash-flow tuff
(HOM).
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