Hörnesite

hornesite

garnet

annabergite

erythrite

Images

Formula: Mg3(AsO4)2.8H2O
Hydrated normal arsenate, vivianite group, forms series with annabergite and with erythrite
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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