Publication Date:
2017-02-15
Description:
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/cm 3 (measured/calculated). It is biaxial, negative, 2Vα = 47(1)/48 (measured/calculated); α = 1.6226(5), β = 1.6852(10), = 1.6982(2); X = c , Y = a , Z = b . The average values of microprobe analyses are (wt.%) P 2 O 5 37.17, SiO 2 0.15, CaO 0.90, Na 2 O 20.06, La 2 O 3 16.44, CeO 2 20.23, Pr 2 O 3 1.40, Nd 2 O 3 3.47, Sm 2 O 3 0.24, Dy 2 O 3 0.06, Y 2 O 3 0.06. 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) Å 3 , Z = 4. The structural formula calculated from the diffraction data and microprobe analysis is Na 7.89 (Ce 0.94 Ca 0.06 ) 1.00 (Ca 0.12 La 1.14 Ce 0.40 Pr 0.10 Nd 0.24 ) 2.00 (PO 4 ) 6 , the simplified formula is Na 8 Ce 4+ REE 2 (PO 4 ) 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).
Print ISSN:
0026-461X
Electronic ISSN:
1471-8022
Topics:
Geosciences
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