Armellinoite-(Ce)

armellinoite-(Ce)

cryptomelane

tilasite

hollandite

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Formula: Ca4Ce4+(AsO4)4.H2O
Arsenate, cerium-bearing mineral
Specific gravity: 4.29 calculated
Hardness: 3 to 3½ estimated
Streak: White
Colour: Pale yellow to brown–yellow
Environments

Metamorphic 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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