| Plain Text | Rønsbo, Jørn G., Balić-Žunić, Tonči, Petersen, Ole V. (2017) Dyrnaesite-(La) a new hyperagpaitic mineral from the Ilímaussaq alkaline complex, South Greenland. Mineralogical Magazine, 81 (1) 103-111 doi:10.1180/minmag.2016.080.075 |
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| Abstract/Notes | The new mineral, dyrnaesite-(La), is found in the Ilímaussaq alkaline complex, South Greenland. The holotype material originates from an arfvedsonite lujavrite sheet as an accessory mineral. Dyrnaesite-(La) is pale yellowish green, with no cleavage and an irregular fracture. Density is 3.68(2)/3.682 g/cm3(measured/ calculated). It is biaxial, negative, 2Vα = 47(1)/48 (measured/calculated); α = 1.6226(5), β = 1.6852(10), γ = 1.6982(2);X=c,Y=a,Z=b. The average values of microprobe analyses are (wt.%) P2O537.17, SiO20.15, CaO 0.90, Na2O 20.06, La2O316.44, CeO220.23, Pr2O31.40, Nd2O33.47, Sm2O30.24, Dy2O30.06, Y2O30.06.The crystal structure was solved from single-crystal X-ray diffraction data. Dyrnaesite-(La) is orthorhombic,Pnma;a= 18.4662(7) Å,b= 16.0106(5) Å,c= 7.0274(2) Å,V= 2077.7(2) Å3,Z= 4. The structural formula calculated from the diffraction data and microprobe analysis is Na7.89(Ce0.94Ca0.06)∑1.00(Ca0.12La1.14Ce0.40Pr0.10Nd0.24)∑2.00(PO4)6, the simplified formula is Na8Ce4+REE2(PO4)6. The crystal structure is related closely to that of vitusite-(Ce), but is distinct from it in several aspects. The five strongest lines of the powder X-ray diffraction pattern are (d Å, (I %), (hkl)); 6.57 (100) (101), 4.62 (40) (301, 230, 400), 3.50 (40) (331), 2.80 (86) (232, 402), 2.67 (54) (060,630). |
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