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Formula: (Ca3REE)[(H2O)2Ca0.5☐0.5]Ti(Si2O7)2(OH)2(H2O)2
Sorosilicate (Si2O7 groups), rinkite group of
the seidozerite supergroup
Crystal System: Monoclinic
Specific gravity: 3.2 to 3.4 measured
Hardness: 4 to 5
Streak: Pale yellow, yellowish green
Colour: Deep reddish brown, brownish green, yellowish; greenish yellow
Solubility: Gelatinises with acids (Dana)
Weakly RADIOACTIVE
Environments:
Mosandrite is an alteration product of rinkite
(Dana).
At Mont Saint-Hilaire, Quebec, Canada, mosandrite occurs in
eudialyte-rich
pegmatites,
sodalite xenoliths and
nepheline syenite
(Dana).
In Greenland mosandrite occurs in sodalite
syenite
(Dana).
The type locality is Låven, Larvik, Vestfold, Norway. Mosandrite-(Ce) specimens often shows signs of
hydrothermal alteration. Here the alteration products may be a mixture of
fluorite, pyrochlore,
calcite, magnetite,
pyrophanite and
lorenzenite
(Mindat).
Mosandrite-(Ce) has been found in many
nepheline syenite
pegmatites in Larvik, where it crystallised early in the
paragenetic sequence. In most of the localities it has been subjected to hydrothermal alteration,
leaving only traces of the original material. Alteration products are
pyrophanite, magnetite,
pyrochlore, fluorite,
calcite, aegirine,
titanite and lorenzenite.
Most mosandrite-(Ce) samples are metamict, due to a small amount of
thorium in the structure
(JWW p161).
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