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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
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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