Natrowalentaite

natrowalentaite

natropharmacosiderite

jarosite

arseniosiderite

Images

Formula: [Fe3+0.5Na0.5(H2O)6][NaAs3+2(Fe3+2.33W6+0.67)(PO4)2O7]
Phosphate, walentaite group, arsenic-bearing mineral
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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