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Formula:
[Fe3+0.5Na0.5(H2O)6][NaAs3+2(Fe3+2.33W6+0.67)(PO4)2O7]
Phosphate, walentaite subgroup,
arsenic-bearing mineral
Crystal System: Orthorhombic
Specific gravity: 2.91 measured, 2.93 calculated
Colour: Greenish yellow
Environments
Metamorphic environments
Hydrothermal environments
Natrowalentaite is a relatively new mineral, approved in 2018 and to date (June 2022) reported only from the
type locality.
Localities
At the type locality, the Griffins Find Gold Mine, Lake Grace Shire, Western Australia, Australia, the deposit
comprises surface enriched, gold-bearing,
quartz–sulphide lodes in a highly metamorphosed
greenstone, which has been intruded by recrystallised
monzogranite. The main ore minerals are
pyrrhotite, löllingite and
arsenopyrite. The rocks have been heavily weathered and the
primary sulphides and arsenides have been converted into a
range of secondary minerals, including
goethite, jarosite,
scorodite,
arseniosiderite and
natropharmacosiderite.
Natrowalentaite occurs on fracture surfaces in iron-stained rock along with
natropharmacosiderite and
jarosite and is a product of
supergene alteration. It forms a dense mass of bright
greenish-yellow blades on a 1.5 mm wide core of brown
natropharmacosiderite. Individual blades are extremely thin
(1–3 μm), typically 10–20 μm wide and up to 200 μm in length.
Because natrowalentaite is present as a surface coating
natropharmacosiderite, that contains arsenic only as
As5+, it seems that more reducing conditions, perhaps resulting from the decomposition of
arsenopyrite, prevailed during the crystallisation of the
natrowalentaite
(AJM 20.1.7–15).
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