Anhydrous carbonate containing halogen, cordylite group, barium- and lanthanum- bearing mineral
Specific gravity: 4.34 measured, 4.329 calculated
Colour: Colorless, honey-yellow, or pinkish yellow
Luminescence: Non-fluorescent in short wave or long wave UV
The type locality, Ust'-Biraya, Biraya Fe-REE ore occurrence, Biraya and Bya Rivers confluence area, Vitim Plateau, Irkutsk Oblast, Russia, comprises a sequence of lens-shaped carbonatite bodies accompanied by fenites.
Cordyite-(La) was discovered as colourless to yellow, irregularly shaped, tabular or short-prismatic hexagonal crystals up to about 3 mm across. They occur in a fine- to medium- grained vein composed mainly of the carbonates aragonite–strontianite, emmonite, strontium-rich calcite, iron-rich dolomite, cordylite-(La) and cordylite-(Ce).
Within the vein, cordylite-(Ce) is more common than cordylite-(La), with only cordylite-(Ce) occurring as single grains, while cordylite-(La) may occur as cores within cordylite-(Ce). Also contained in the vein and in direct association with cordylite-(La) are baryte, biraite-(Ce), niobium-rich chevkinite-(Ce), fergusonite-(Nd), ancylite-(Ce), ancylite-(La), daqingshanite-(Ce), bastnäsite-(Ce), hydroxylbastnäsite-(Ce), carbocernaite, monazite-(Ce), talc, thorite, humite, galena, pyrite and pyrrhotite. Minerals in the outer zone of the vein near the fenite include tremolite, winchite, ferriallanite-(Ce), törnebohmite-(Ce), belkovite, ancylite-(La), strontianite, fergusonite-(Ce), zero-valent-dominant light-rare-earth-element bearing pyrochlore and nioboaeschynite-(Ce) (CM 50.5.1281-1290).
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