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Formula: Ca4Ce4+(AsO4)4.H2O
Arsenate, cerium-bearing mineral
Crystal System: Tetragonal
Specific gravity: 4.29 calculated
Hardness: 3 to 3½ estimated
Streak: White
Colour: Pale yellow to brown–yellow
Environments
Armellinoite-(Ce) is a relatively new mineral, approved in 2018 and to date (March 2022) reported
only from the type locality.
Localities
At the type locality. the Montaldo mine, Borgata Oberti, Montaldo di Mondovì, Cuneo Province, Piedmont, Italy,
armellinoite-(Ce) was discovered in
iron-manganese ore in
metaquartzite. It occurs as very small and rare, pale yellow
to brown–yellow pseudo-octahedral translucent crystals hosted by a matrix of
quartz, hematite,
cryptomelane/hollandite,
tilasite, muscovite,
braunite and
montmorillonite
(MM 85.6.901-909).
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