凤成石:异性石族矿物N(5)位贫钠的空位类似物新种

Fengchengite: A New Species with the Na-Poor but Vacancy-Dominante N(5) Site in the Eudialyte Group

作为异性石族矿物新种凤成石是首个该族已知成员中N(5)位贫Na且以空位居优的类似物,其理想化学式为:Na_(12)□_3Ca_6(Fe^(3+),□)_3Zr_3Si(Si_(25)O_(73))(H_2O)_3(OH)_2。它发现于我国东北辽宁省凤城市赛马钠质碱性正长岩内,多呈它形-半自形晶产出,单个晶体粒径1~7mm,最大粒径者>1.5cm。与之共生的矿物有微斜长石、正长石、钠长石、霞石和钠角闪石亚族矿物、霓石、榍石和闪叶石族矿物、"贫钠的层硅钛铈矿"("Napoor rinkite")、钛铌钙铈矿、钠锆石、锆石、铁金云母、氟磷灰石、富稀土的羟硅磷灰石和何作霖矿等。矿物为半透明-透明,玻璃光泽,条痕白色,性脆,摩氏硬度约5,偶见不完全解理和裂开,一轴晶正光性。N_e=1.607,N_o=1.603。凤成石属三方晶系,具R3m空间群;a=1.42467(6)nm,c=3.00330(2)nm,V=5.27908(50)nm^3,Z=3。6条强粉晶衍射线[面网间距(衍射强度)(指标化)]是:0.7186(55)(110),0.5761(44)(113),0.4187(53)(123),0.3201(47)(028),0.2978(61)(135)和0.2857(100)(044)。16点矿物成分的电子探针等分析均值为:Na_2O 11.64%,K_2O 0.52%,CaO 8.96%,MgO 0.07%,SrO_3.53%,BaO 0.02%,MnO0.10%,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%,总量100.14%。根据晶体结构精测和(O+OH+F+Cl)=78计算的矿物经验化学式:[(Na_(3.00)Na_(3.00))Σ_(6.00)(Na_(5.28)K_(0.33)□_(0.39))]_(12.00)□_(2.71)Sr_(0.20)REE_(0.09))_(3.00)Ca_(4.80)Sr_(0.82)Fe_(0.29)^(2+)Mg_(0.05)Mn_(0.04)^(2+))_(6.00)(Fe_(2.25)^(3+)Mn_(0.35)^(3+)Cr_(0.08)□_(0.32))_(3.00)(Zr_(2.86)Ti_(0.09)Nb_(0.05))_(3.00)(Si_(0.87)Ti_(0.05)□_(0.08))_(1.00)Si_(1.00)(Si_(24.00)O_(72.00))[(H_2O)_(2.93)O_(1.00)(OH)_(0.07)]_(3.00)[(OH)_(1.04)Cl_(0.96_]_(2.00)。矿物实测密度2.93g/cm^3;计算密度2.88g/cm^3。基于野外和室内研究,借鉴有关合成异性石族矿物的实验资料,凤成石由一类富REE、U、Th、Zr、和挥发分的钠质碱性正长岩岩浆直接结晶而成。

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 Na12 口3Ca6 （Fe^3＋, 口） 3 Zr3 Si （ Si25 O73 ） （ H2O） 3 （ OH ） 2, is the Na-poor but vacancy-dominant analogue at the N（5） site in the known menbers in the group minerals. It occurs as anhedral to subhedral crystals. Most indeividual 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, sphene, 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 of 5.0±.It has no discernable cleavp age or parting and an uneven fracture. It is uniaxial negative with e= 1.607,ω= 1.603. It is trigonal, space grou R3m,a 14. 2467（6）A and c 30. 033 0（2）A, V 5279.08 （50）A3, Z = 3.The six strongest X-ray powder-diffraction lines, measured for fengchengite [din A（1）（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 Na20 11.64%, K20 0.52%, CaO 8.96%, MgO 0.07%, SrO 3.53%, BaO 0.02%, MnO 0. 10%, FeO 0.69%, Mn203 0.92%, Fe203 5.98%, La203 0. 12%, Ce203 0.23%, Nd2030.13%, Sc2030.01%, TiO20.38%, ZrO2 11.72%, Nb2O50.23%, SiO251.73%, C1, 1. 13%, H20 2.09%, O= CI-0. 26%, total 100. 14 wt.%.The empirical formula of fengchengite, based on （ O＋OH＋F＋C1 ） = 78 anions pfu from the crystal-structure refinement, is： [ （ Na3.00 Na3.00） ∑6.00（ Na5.28 K0.33口0.39 ）∑12.00（ 口12.7, Sr0.20 REE0.09 ） 23.00 （ Ca4.80 Sro.s2 Fe0.29^2＋ Mg0.05 Mn0.04^2＋ ） ∑6.00 （Fe2.＋25^3＋ Mn30.35^3＋ Cr0.08口0.32 ） ∑3.00 （ Zr2.86 Ti0.09 Nb0.05 ） ∑3.00 （ Si0.87 Ti0.05 口0.08 ） ∑1.00 Si （ Si24.00 O73.00 ） [ （U20）2.93（OH）0.07 ] 23.00[ （OH）1.04 Cl0.96 ] ∑2.00.Dmeas =2.93 g/cm^3; Dcale= 2.88 g/cm^3.The new species is named after its locality. In the saima agpaite, fengchengite occurs as accessory or/and rock- forming 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.