Referenza:
▪ Shen, G., Xu, J., Yao, P., Li, G. (2017): Fengchengite: A New Species with the Na-Poor but Vacancy-Dominante N(5) Site in the Eudialyte Group. Acta Mineralogica Sinica, 2017-Z1.
Abstract:
As a new species of the eudialyte group from the Saima agpaite and its pegmatitic facies, situated about 60 km noth-northeast of Fengcheng City, Liaoning Province, northeastern China. Fengchengitehe, ideally Na_(12)□_3Ca_6( Fe~(3+),□)_3Zr_3Si( Si_(25)O_(73))( H_2O)_3(OH)_2, is the Na-poor but vacancy-dominant analogue at the N( 5) site in the known members in the group minerals. It occurs as anhedral to subhedral crystals. Most individual grains are 1 ~ 7 mm in diameter, the largest grain size 15 mm. Associated minerals include microline, orthociase, albite, nepheline, sodic amphibole subgroup minerals, aegirine, lamprophyllite group minerals,"Na-poor rinkite", loparite, catapleiite, zircon, titanite, irony phlogopite, fluorapatite, REE-rich hydoxylellestadite and hezuolinite etc. It is transparent to translucent with a vitreous luster and white streak, and brittle with a Mohs hardness of5. 0±.It has no discernable cleavage or parting and an uneven fracture. It is uniaxial negative with ε = 1. 607, ω = 1. 603. It is trigonal, space group R3m, a 14.2467( 6) and c 30.033 0( 2), V 5279.08( 50), Z = 3.The six strongest X-ray powder-diffraction lines,measured for fengchengite [d in ( I)( hkl) ] are: 7. 186( 55)( 110),5. 761( 44)( 113),4. 187( 53)( 123),3. 201( 47)( 028),2. 978( 61)( 135) and 2. 857( 100)( 044).An average result of sixteen electron-microprobe etc. analyses,gave Na_2O 11. 64%,K_2O 0. 52%,CaO 8. 96%,MgO 0. 07%,SrO_3. 53%,BaO0. 02%,MnO 0. 10%,FeO 0. 69%,Mn_2O_30. 92%,Fe_2O_35. 98%,La_2O_30. 12%,Ce_2O_30. 23%,Nd_2O_30. 13%, Sc_2O_30. 01%, TiO_20. 38%, ZrO_211. 72%,Nb_2O_50. 23%, SiO_251. 73%, Cl,1. 13%,H_2O 2. 09%,O ≡ Cl-0. 26%,total 100. 14 wt.%. The empirical formula of fengchengite, based on(O +OH + F + Cl) = 78 anions pfu from the crystal-structure refinement, is: [( Na_(3. 00)Na_(3. 00))Σ_(6. 00_( Na_(5. 28)K_(0. 33)□_(0. 39)) ]Σ_(12. 00)( □_(2. 71)Sr_(0. 20_REE_(0. 09))Σ_(3. 00)( Ca_(4. 80_Sr_(0. 82)Fe_(0. 29)~(2+)Mg_(0. 05)Mn_(0. 04)~(2+))Σ_(6. 00)( Fe_(2. 25)~(3+)Mn_(0. 35)~(3+)Cr_(0. 08)□_(0. 32))Σ_(3. 00)( Zr_(2. 86)Ti_(0. 09)Nb_(0. 05))Σ_(3. 00)( Si_(0. 87)Ti_(0. 05)□_(0. 08))Σ_(1. 00)Si( Si_(24. 00)O_(73. 00))[( H_2O)_(2. 93)(OH)_(0. 07)]Σ_(3. 00)[(OH)_(1. 04)Cl_(0. 96)]Σ_(2. 00). Dmeas. = 2. 93g/cm~3; Dcalc. = 2. 88g/cm3. The new species is named after its locality. In the Saima agpaite, fengchengite occurs as accessory or/and rockforming mineral, locally, its modal content ≥90%. By the field, laboratory studies and the related experimental synthetic data of eudialyte group minerals, fengchengite crystallized directly from a REE-,U-,Th-and Zr-rich agpaitic magma enriched in volatile components.
NB: Reference added to the fengchengite page.
▪ Shen, G., Xu, J., Yao, P., Li, G. (2017): Fengchengite: A New Species with the Na-Poor but Vacancy-Dominante N(5) Site in the Eudialyte Group. Acta Mineralogica Sinica, 2017-Z1.
Abstract:
As a new species of the eudialyte group from the Saima agpaite and its pegmatitic facies, situated about 60 km noth-northeast of Fengcheng City, Liaoning Province, northeastern China. Fengchengitehe, ideally Na_(12)□_3Ca_6( Fe~(3+),□)_3Zr_3Si( Si_(25)O_(73))( H_2O)_3(OH)_2, is the Na-poor but vacancy-dominant analogue at the N( 5) site in the known members in the group minerals. It occurs as anhedral to subhedral crystals. Most individual grains are 1 ~ 7 mm in diameter, the largest grain size 15 mm. Associated minerals include microline, orthociase, albite, nepheline, sodic amphibole subgroup minerals, aegirine, lamprophyllite group minerals,"Na-poor rinkite", loparite, catapleiite, zircon, titanite, irony phlogopite, fluorapatite, REE-rich hydoxylellestadite and hezuolinite etc. It is transparent to translucent with a vitreous luster and white streak, and brittle with a Mohs hardness of5. 0±.It has no discernable cleavage or parting and an uneven fracture. It is uniaxial negative with ε = 1. 607, ω = 1. 603. It is trigonal, space group R3m, a 14.2467( 6) and c 30.033 0( 2), V 5279.08( 50), Z = 3.The six strongest X-ray powder-diffraction lines,measured for fengchengite [d in ( I)( hkl) ] are: 7. 186( 55)( 110),5. 761( 44)( 113),4. 187( 53)( 123),3. 201( 47)( 028),2. 978( 61)( 135) and 2. 857( 100)( 044).An average result of sixteen electron-microprobe etc. analyses,gave Na_2O 11. 64%,K_2O 0. 52%,CaO 8. 96%,MgO 0. 07%,SrO_3. 53%,BaO0. 02%,MnO 0. 10%,FeO 0. 69%,Mn_2O_30. 92%,Fe_2O_35. 98%,La_2O_30. 12%,Ce_2O_30. 23%,Nd_2O_30. 13%, Sc_2O_30. 01%, TiO_20. 38%, ZrO_211. 72%,Nb_2O_50. 23%, SiO_251. 73%, Cl,1. 13%,H_2O 2. 09%,O ≡ Cl-0. 26%,total 100. 14 wt.%. The empirical formula of fengchengite, based on(O +OH + F + Cl) = 78 anions pfu from the crystal-structure refinement, is: [( Na_(3. 00)Na_(3. 00))Σ_(6. 00_( Na_(5. 28)K_(0. 33)□_(0. 39)) ]Σ_(12. 00)( □_(2. 71)Sr_(0. 20_REE_(0. 09))Σ_(3. 00)( Ca_(4. 80_Sr_(0. 82)Fe_(0. 29)~(2+)Mg_(0. 05)Mn_(0. 04)~(2+))Σ_(6. 00)( Fe_(2. 25)~(3+)Mn_(0. 35)~(3+)Cr_(0. 08)□_(0. 32))Σ_(3. 00)( Zr_(2. 86)Ti_(0. 09)Nb_(0. 05))Σ_(3. 00)( Si_(0. 87)Ti_(0. 05)□_(0. 08))Σ_(1. 00)Si( Si_(24. 00)O_(73. 00))[( H_2O)_(2. 93)(OH)_(0. 07)]Σ_(3. 00)[(OH)_(1. 04)Cl_(0. 96)]Σ_(2. 00). Dmeas. = 2. 93g/cm~3; Dcalc. = 2. 88g/cm3. The new species is named after its locality. In the Saima agpaite, fengchengite occurs as accessory or/and rockforming mineral, locally, its modal content ≥90%. By the field, laboratory studies and the related experimental synthetic data of eudialyte group minerals, fengchengite crystallized directly from a REE-,U-,Th-and Zr-rich agpaitic magma enriched in volatile components.
NB: Reference added to the fengchengite page.