Hydrated normal phosphate, meta-autunite group
Specific gravity: 3.62 calculated
Hardness: 2 to 2½
Colour: Lemon yellow
Luminescence: Fluoresces yellow green in short wave and long wave UV
Metanatroautunite is a secondary uranium mineral
At the Fairview Quarry, Robertstown, North Mt Lofty Ranges, Mt Lofty Ranges, South Australia, metanatroautunite occurs as crusts of thin platy crystals to 3 mm coating seams and lining cavities in phosphate rock. Associated minerals include natrodufrénite and cyrilovite (AJM 17.1.20).
The Lake Boga granite, Lake Boga, Swan Hill Rural City, Victoria, Australia, is a very large intrusion formed about 365 million years ago. The entire outcrop of the granite is overlain by sediments in places up to several hundred meters thick. The sole exposure into the granite is the Lake Boga quarry, where the sediment is only a few metres thick. The uppermost levels of the granite exhibit aplite veins, pods of pegmatite, and numerous miarolitic cavities, features that are characteristic of the uppermost levels of a granite magma intruded to shallow crustal levels. (R&M 97.1.28-32).
Metanatroautunite from this locality forms crystals and clusters to 4 mm across on limonite-coated joint planes and in a miarolitic cavity in granite. Rare intergrowths with saléeite and torbernite occur (HOM, AJM 10.1.29-31).
At the Kuruk U Deposit, Khodzhent, Sughd, Tajikistan, metanatroautunite occurs in the oxidised zone of a uranium deposit in a granodiorite massif, associated with schoepite, gypsum, kaolinite and limonite (HOM).
Boomerang Lake, Menangina Station, Menzies Shire, Western Australia, is a playa (flat area at the lowest part of an undrained desert basin), situated in a semi-arid region with hot summers and mild winters. The playa forms part of a chain of lakes that are usually dry, and there is surface water flow only after exceptional rains. Metanatroautunite has been found in a small area close to the northern shore of the lake in saline, gypsum-rich mud, mostly at depths of 30-100 cm. It appears as bright greenish yellow disseminations, fracture coatings and veinlet infillings in the red-brown mud. Also present are quartz, gypsum, halite and a uranium oxide, probably uraninite (AM 66.1068-1072).
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