Monteregianite-(Y) , Aegirine , Pectolite Locality: Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry), Mont Saint-Hilaire , Rouville RCM, Montérégie , Québec , Canada ( Locality at mindat.org ) A VERY fine example of this rare species from MSH, consisting of sharp parallel crystals to 1.4 cm in a cluster atop contrasting matrix of pectolite. The Monteregianite has excellent waxy lustre for the species, and the crystals are of a size that would have to be considered exceptional and difficult to obtain in such form. 4 x 3 x 2 cm — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Monteregianite-(Y)
Monteregianite-(Y) is an IMA-recognized mineral species in the silicate class, with the chemical formula KNa₂YSi₈O₁₉·5H₂O.
It crystallizes in the monoclinic crystal system (space group Bmab). It is a member of the Rhodesite structural group.
Key properties: Mohs hardness 3.5; specific gravity 2.42; White streak; Vitreous to silky luster; optically biaxial.
IMA symbol Mreg-Y, IMA status: approved, named in 1972.
Found in miarolitic cavities, metamorphosed inclusions, and rheomorphic breccias in nepheline syenite in an intrusive alkalic gabbro-syenite complex.
It is found associated with Calcite, pectolite, microcline, albite, aegirine, arfvedsonite, phlogopite, fluorite, quartz, ekanite, sepiolite, ashcroftine, lorenzenite, narsarsukite.
The name refers to the Monteregian Hills, of which Mont Saint-Hilaire is one, and yttrium in the composition.