ahlfeldite


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ahlfeldite

[äl′fel‚dīt]
(mineralogy)
(Ni,Co)SeO3·2H2O A triclinic mineral identified as green to yellow crystals with a reddish-brown coating, consisting of a hydrous selenite of nickel.
References in periodicals archive ?
The Pacajake mine, hidden high in the Cordillera Oriental of the Bolivian Andes, is famous for its rare selenides, selenates and selenites, and is the type locality for penroseite, ahlfeldite, olsacherite and mandarinoite.
Ahlfeldite, a hydrated nickel selenite, was described as a new mineral species from Pacajake by Herzenberg and Ahlfeld (1935).
Ahlfeldite is rare, occurring on only a few samples as an alteration product of penroseite in crystalline crusts 1 to 1.5 mm thick covering areas of only a few square millimeters or filling small cavities.
Ahlfeldite is monoclinic and the crystals are elongated along the c-axis or flattened on {110}.
The first adequate description of ahlfeldite from Pacajake was given by Goni and Guillemin (1953) of the Sorbonne.
It was described by Palache (1937) as an acicular, white oxidation product of penroseite, and by Ahlfeld and Munoz Reyes (1955) as occurring with ahlfeldite, chalcomenite and olsacherite in cavities in decomposed penroseite.
Cobaltomenite occurs at Pacajake in solid solution with ahlfeldite; the name cobaltomenite is used when the cobalt content is greater than or equal to the nickel content.
The mineral was first observed at Pacajake by Herzenberg and Ahlfeld (1935) coating ahlfeldite which fills fractures in penroseite.
They observed that it occurs in only a few samples as small, colorless acicular crystals on ahlfeldite and limonite in cavities formed by the weathering of penroseite.
Herzenberg (1944) thought the red-brown coating on ahlfeldite, which was removed by nitric acid, to be amorphous selenium formed by oxidation of ahlfeldite on exposure to air, however, there is no evidence to support this speculation.
Oxidation of penroseite gave rise to ahlfeldite (Ni), cobaltomenite (Co) and chalcomenite (Cu), while clausthalite gave the secondary lead minerals cerussite, molybdomenite, olsacherite and perhaps also wulfenite.
The mineral ahlfeldite, a hydrated nickel selenite discovered at the Pacajake mine in Bolivia, was named in his honor in 1935.