Formula: (Mn,Ca)Mn2Ca2(AsO3OH)2(AsO4)2.4H2O
Hydrated acid arsenate, hureaulite group, manganese-bearing mineral
Specific gravity: 3.20
Hardness: 4
Streak: White
Colour: Colourless, orange to light pink
Solubility: Soluble in hydrochloric acid
Common impurities: Zn,Ca,Fe

Metamorphic environments
Hydrothermal environments


At the type locality, Ste Marie-aux-Mines, Colmar-Ribeauvillé, Haut-Rhin, Grand Est, France, villyaellenite has been identified on a single specimen that also contains the second reported occurrence of ogdensburgite here. The villyaellenite occurs as orange-pink, prismatic crystals to 4 cm that form a compact spray mostly filling a vug. The walls of the vug are coated with alternating layers of arseniosiderite and ogdensburgite. An aureole of chalcophanite surrounds the vug and extends into the host rock, which is a limonitic gossan. Crystals and stringers of colourless to pale green adamite are embedded in the limonite, chalcophanite, and the layered arseniosiderite-ogdensburgite assemblage (AM 73.1172-1178). The villyaellenite is a rare post-mine low-temperature reaction product of carbonate gangue with arsenic-bearing solutions. Other associated minerals include fluckite, picropharmacolite, pharmacolite and arsenic (AM 71.1547, HOM).

At Mapimí, Mapimí Municipality, Durango, Mexico, villyaellenite has been found on a museum specimen from the oxidised zone of an arsenic-rich base metal deposit. Associated minerals include ogdensburgite, arseniosiderite, chalcophanite, adamite and iron-manganese oxides (HOM, Dana).

At Sterling Mine, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex County, New Jersey, USA, villyaellenite has been reported from a metamorphosed stratiform zinc orebody as transparent orange-pink crystals in flattened, 7-mm diameter, aggregates. Found on calcite-bearing willemite-franklinite ore and associated with manganoan calcite, willemite and franklinite. Other unusual phases found in the same part of the Sterling Hill deposit include ogdensburgite, sterlinghillite, wallkilldellite and a manganese-bearing adamite (AM 73.1172-1178, HOM).
According to Mindat (accessed April 2021) the occurrence of villyaellenite at this locality is now discredited.

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