Tectosilicate (framework silicate)
Specific gravity: 2.32
Common impurities: Mg,Ca,Ba,Na,K
Hot Spring deposits
Buddingtonite occurs in plagioclase altered by ammonium-bearing waters
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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