Illoqite-(Ce), Na₂NaBaCeZnSi₆O₁₇, a new member of the nordite supergroup from Ilímaussaq alkaline complex, South Greenland.

AbstractThe new mineral, illoqite-(Ce), with the ideal formula Na2NaBaCeZnSi6O17, has been discovered in the Taseq Slope, Ilímaussaq Alkaline Complex, Southern Greenland. Illoqite-(Ce) occurs in a hyperalkaline ussingite vein closely related to one of the largest ussingite veins in the Ilímaussaq complex. The associated minerals are aegirine, arfvedsonite, a britholite-group mineral, epistolite, chkalovite, lueshite, Mn-rich pectolite group member and steenstrupine-(Ce). Illoqite-(Ce) crystallises as either single euhedral crystals up to 150 μm in size or radiating aggregates consisting of a few or many crystals. The aggregates are up to 200 μm in diameter. Illoqite-(Ce) can occur as scattered small groups of crystals or aggregates, but sometimes they occur in high concentrations creating clusters or bands almost completely consisting of illoqite-(Ce). The empirical formula on the basis of 17 anions is Na2.00Na1.00(Ba0.59Sr0.32Ca0.04Na0.03)Σ0.98(Ce0.68La0.31Nd0.09Pr0.04)Σ1.12(Zn0.42Fe0.34Li0.14Mn0.09)Σ0.99Si5.97O17, with the simplified formula being Na2Na(Ba,Sr)(Ce,La,Nd)(Zn,Fe,Li)Si6O17. Illoqite-(Ce) exhibits sector zoning between elements Sr and Ba. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R1 = 2.46% using 1902 unique reflections. Illoqite-(Ce) is orthorhombic, Pcca, with a = 14.5340(7), b = 5.2213(1), c = 19.8270(4) Å, V = 1507.25(6) Å3 and Z = 4. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 7.266 (79) (200), 4.688 (44) (104), 4.241 (64) (210), 3.486 (79) (114), 3.340 (52) (312), 2.986 (67) (410), 2.882 (100) (314) and 2.789 (44) (016). Illoqite-(Ce) is a new member of the nordite supergroup and is named after the Greenlandic word illoq, meaning cousin, in allusion to the mineral's close relation to nordite-(Ce).