Both are sorosilicates (Si2O7 groups), thortveitite group
Specific gravity: keiviite-(Y) 4.45, keiviite-(Yb) 5.95
Hardness: 4 to 5 (both)
Streak: White (both)
Colour: keiviite-(Y) colourless, white, pink, brown keiviite-(Yb) colourless
Both occur in amazonite pegmatites. Keiviite-(Y) occurs in fissures in
quartz and fluorite and keiviite-(Yb) occurs with
Minerals associated with keiviite-(Y) include keiviite-(Yb), thalénite-(Y), xenotime, bastnäsite, kuliokite-(Y), quartz, and fluorite (HOM). Two generations of keiviite-(Yb) occur together, associated with fluorite, bastnäsite, hingganite and wulfenite (HOM).
The type locality for both minerals is the Ploskaya Mountain, Western Keivy Massif, Keivy Mountains, Lovozersky District, Murmansk Oblast, Russia, where they occur in an amazonite-bearing granite pegmatite.
Keiviite-(Y) occurs in fissures in quartz and fluorite, or on keiviite-(Yb) associated with thalénite-(Y), xenotime, bastnäsite and kuliokite-(Y) (Dana, AM 73.191-192).
Keiviite-(Yb) occurs within fluorite. Two generations of keiviite-(Yb) are present, associated with fluorite, bastnäsite and hingganite (Dana).
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