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Formula: NaMg4(AsO4)3
Anhydrous arsenate, forms a series with
udinaite
Specific gravity: 3.816 calculated
Hardness: 3½:
Streak: White
Colour: Beige, pale brownish, brownish-yellowish or greyish-brownish
Epitaxy: Interesting double epitactic intergrowths were observed: “ribbed” parallel aggregates of small, flattened
forsterite crystals epitactically overgrow a larger prismatic
anhydrite crystal and crystals of
udinaite or arsenudinaite epitactically overgrow
forsterite
(Mindat).
Environments
Arsenudinaite is a relatively new mineral, approved in 2018 and to date (September 2025) reported only from
the type locality.
Localities
At the type locality, the Arsenatnaya fumarole, Second scoria cone, Northern Breakthrough, Great Fissure eruption,
Tolbachik Volcanic field, Milkovsky District, Kamchatka Krai, Russia, minerals of the
udinaite–arsenudinaite series were found. Strong fumarolic activity
occurs here currently, and the active, hot oxidising type fumarole is characterised by an outstanding mineral
diversity.
The type specimens of both udinaite and arsenudinaite were collected
from 3 to 4 m deep under the day surface, the hottest zone of the Arsenatnaya fumarole. The temperatures in this area
measured during collecting were 450 to 470oC. Sublimate incrustations in this zone are up to 4 cm thick
and usually mainly consist of anhydrite,
diopside and hematite, typically
with significant amounts of
arsenate–vanadate
garnets of the
berzeliite–schäferite series
and svabite. Udinaite and
arsenudinaite are associated, besides with these minerals, with one another and with
calciojohillerite,
tilasite, reznitskyite,
ludwigite,
rhabdoborite group borates,
forsterite,
magnesioferrite,
fluorapatite, pliniusite,
arsenowagnerite,
wagnerite,
powellite, scheelite, and
baryte.
In July 2021 in the upper part of this zone, the As-richest variety of arsenudinaite close to the end-member
NaMg4(AsO4)3 was found. It is associated with
hematite,
fluorophlogopite,
sanidine, forsterite,
enstatite,
calciojohillerite and
fluorapatite–svabite series
members.
(Minerals 12.7.850)
Arsenudinaite from the Arsenatnaya fumarole -
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