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


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The new mineral, illoqite-(Ce), with the ideal formula Na2NaBaCeZnSi6O17, has been discovered in the Taseq Slope, Ilimaussaq Alkaline Complex, Southern Greenland. Illoqite-(Ce) occurs in a hyperalkaline ussingite vein closely related to one of the largest ussingite veins in the Ilimaussaq 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 mu m in size or radiating aggregates consisting of a few or many crystals. The aggregates are up to 200 mu m 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)(sigma 0.98)(Ce0.68La0.31Nd0.09Pr0.04)(sigma 1.12)(Zn0.42Fe0.34Li0.14Mn0.09)(sigma 0.99)Si5.97O17, 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 R-1 = 2.46% using 1902 unique reflections. Illoqite-(Ce) is orthorhombic, Pcca, with a = 14.5340(7), b = 5.2213(1), c = 19.8270(4) angstrom, V = 1507.25(6) angstrom(3) and Z = 4. The strongest lines of the powder X-ray diffraction pattern [d, angstrom (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).
illoqite-(Ce), new mineral, nordite supergroup, Ilimaussaq Alkaline Complex, crystal structure, REE-minerals, sector zoning
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