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Formula: (Mn,Ca)Mn2Ca2(AsO3OH)2(AsO4)2.4H2O
Hydrated acid arsenate,
hureaulite group,
manganese-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.20 measured, 3.24 calculated
Hardness: 4
Streak: White
Colour: Colourless, orange to light pink
Solubility: Soluble in hydrochloric acid
Common impurities: Zn,Ca,Fe
Environments
Metamorphic environments
Hydrothermal environments
Localities
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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