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Formula: KNa2YSi8O19.5H2O
Phyllosilicate (sheet silicate), forms a series with wickenburgite
Crystal System: Monoclinic
Specific gravity: 2.42 measured, 2.391 calculated
Hardness: 3½
Streak: White
Colour: Colourless, white, grey, rarely mauve or pale green
Luminescence: Bright green fluorescence in short-wave UV (Dana)
Environments
Plutonic igneous environments
Metamorphic environments
Monteregianite is a rare mineral that to date (December 2021) has been found only at the type locality
Localities
At the type locality, the Poudrette quarry, Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Quebec, Canada,
monteregianite occurs as acicular crystals in radiating clusters and as groups of tabular crystals. The crystals
are found in miarolitic cavities and thermally metamorphosed inclusions and
breccias in
nepheline syenite, in an intrusive alkalic
gabbro-syenite complex.
The monteregianite is usually associated with calcite,
pectolite, microcline,
albite, aegirine,
arfvedsonite and minor amounts of
phlogopite, fluorite,
quartz, ekanite,
sepiolite, ashcroftine,
lorenzenite, narsarsukite,
natrolite, harmotome,
apophyllite, molybdenite and
pyrite
(CM 16.561-565).
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