Eudialyte: Gemstone Information
Transparent to translucent red to reddish brown eudialyte (very fine though small bright red crystals come from Mt Saint Hilaire, Quebec, Canada) has sometimes been faceted. Eudialyte is Na4(Ca,Ce)2(Fe2,Mn2) ZrSi6O17(OH,Cl)2 and forms short rhombohedral to prismatic crystals of the trigonal system. The hardness is 5–6 and the SG 2.74–3.10. The RI is 1.588–1.636 and 1.588–1.638 with a birefringence of 0.004, uniaxial positive or negative. Absorption lines may be seen at 595, 527 and 523 nm. Eudialyte is soluble in acids. It occurs in nepheline syenites, alkalic granites and associated pegmatites. Apart from the Mt St Hilaire deposit, facet-grade material has also been found in Quebec at Kipawa Complex, Sheffield Lake,Temiscamingue County.