Cyrilovite

cyrilovite

dufrenite

frondelite

phosphosiderite

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Formula:NaFe3+3(PO4)2(OH)4.2H2O
Hydrated phosphate containing hydroxyl, wardite group
Crystal System: Tetragonal
Specific gravity: 3.081 to 3.096 measured, 3.114 calculated
Hardness: 4
Streak: Yellow
Colour: Bright yellow, honey-yellow, orange to brownish yellow, brown
Environments

Pegmatites

Cyrilovite is a rare accessory mineral in some oxidising phosphate-bearing granite pegmatites and iron deposits (HOM).
Associated minerals include dufrénite, frondelite, phosphosiderite, leucophosphite, whitlockite, kingsmountite, triphylite, rockbridgeite, strengite, jahnsite, montgomeryite, millisite, wardite, apatite and wavellite (HOM).

At the Mount Deverell variscite deposit, Milgun Station, Western Australia, cyrilovite has been found as crusts on fracture surfaces in siltstone, associated with mitridatite and leucophosphite. The variscite deposits are hosted by marine sedimentary rocks (AJM 20.2.24).

At the type locality, the Cyrilov phosphate pegmatite, Křižanov, Žďár nad Sázavou District, Vysočina Region, Czech Republic, cyrilovite occurs in a pegmatite (Mindat).

The Emmons pegmatite, Uncle Tom Mountain, Greenwood, Oxford County, Maine, USA is complexly zoned with a wall zone comprising K-feldspar, quartz, almandine and schorl. The intermediate zones comprise K-feldspar, quartz, muscovite and altered spodumene. A quartz-rich core is present but is poorly exposed (CM 56.543-553 2018).
Bright yellow crystals of cyrilovite up to 1 mm in size have been discovered in the secondary phosphate assemblages derived from the alteration of lithiophilite. The crystals occur in a mineral assemblage dominated by Fe3+-rich mineral species of strunzite, jahnsite-group members, kryzhanovskite, laueite, pseudolaueite, stewartite, beraunite, mitridatite and strengite. The cyrilovite likely formed under oxidising conditions between 300°C and 100°C from primary phosphates of the lithiophilite-triphylite series. Initially, numerous species containing both Fe3+ and Mn2+ occur, such as strunzite and stewartite, but eventually the assemblages transform to essentially manganese-free species such as strengite and phosphosiderite, or species containing the alkali ions Na or K, such as cyrilovite, leucophosphite or kapundaite (R&M 96.6.559-560).

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