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Formula: Mg3(AsO4)2.8H2O
Hydrated arsenate,
vivianite group, forms series with
annabergite and with
erythrite
Crystal System: Monoclinic
Specific gravity: 2.57 to 2.73 measured, 2.57 calculated
Hardness: 1
Colour: White; colourless in transmitted light
Solubility: Soluble in acids
Environments
Metamorphic environments
Hydrothermal environments
Hörnesite occurs in oxidised arsenic ore deposits, on fractures in
serpentine, in marble
xenoliths and as post-mine efflorescence on tunnel walls or dump rocks
(Mindat).
Localities
At the Fiano tuff quarries, Nocera Inferiore, Salerno, Campania, Italy, hörnesite occurs in
limestone blocks, thermally metamorphosed, in a volcanic
tuff
(Webmin).
At the type locality, the Ciclova deposit, Ciclova Română, Caraş-Severin County, Romania, hörnesite occurs in
the oxidised copper-molybdenum
deposit. Associated Minerals include garnet and
calcite
(Mindat).
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