Tveitite-(Y) and REE-enriched fluorite from amazonite pegmatites of the Western Keivy, Kola Peninsula, Russia: Genetic crystal chemistry of natural Ca,REE-fluorides
Tveitite-(Y) and REE-enriched fluorite from amazonite pegmatites of the Western Keivy, Kola Peninsula, Russia: Genetic crystal chemistry of natural Ca,REE-fluorides
复制标题
俄罗斯科拉半岛凯维西部天河伟晶岩中富含钙镁矿 (Y) 和稀土元素的萤石：天然钙、稀土元素氟化物的遗传晶体化学
DOI：
10.1134/s1075701509070083
复制
发表时间：
2009
影响因子：
0.7
通讯作者：
A. Voloshin
中科院分区：
文献类型：
--
作者：
I. Pekov;N. Chukanov;N. N. Kononkova;O. Yakubovich;W. Massa;A. Voloshin
Tveitite-（Y）为豆荚状，直径可达10 cm。俄罗斯科拉半岛西凯维的罗夫戈拉，与碱性花岗岩有关的钠长石-石英-亚马逊伟晶岩脉中。钙黄长石-（Y）颗粒（高达4 cm）是两种同构变体Ca9.5Na1.7Y5.2Ln 2.0F42.6和Ca11.4Na1.9Y4.4Ln 1.4F42.0的平行微共生体。理想结构式（Z = 3）为（Y，Na）6（Ca，LREE）6（Ca，Na，HREE）6（Ca，Na）F42，简化结构式为（Ca，REE，Na）13（Y，Na）6 F42，空间群为R$$
\bar 3
$$a = 17.020，c = 9.679先令。[Lanthanoides在本文中缩写为Ln，而Ln + Y为REE]。用电子探针、X射线粉末衍射和红外光谱对9个含0 ~ 18mol%（REE）F_3的萤石样品进行了分析。首次测定了天然氟钇矿的晶体结构（Raniso = 1.47%）：Fm_（3 m），a = 5.493 μ m，结构式为（Ca0.82Y0.12Ln0.06）F_（2.15）。较早发表的和新的数据表明，含（REE）F_3> 20mol%的钇萤石和LREE > Y（HREE）的富稀土萤石在室温条件下是介稳的。在自然界中，钇矿-（Y）是（REE）F_3> 20mol%的亚稳钇矿固态转变的产物。推测的原生相可能已溶出为组成可变的tveitite-（Y）或在正常条件下稳定的tveitite-（Y）+ yttrofluorite。钙钛矿-（Y）的形成不仅需要Y的原生相富集，而且需要LREE和HREE作为稳定混合物的原生相富集，LREE和HREE在不同类型的Ca优势结构位上呈规则分布。钇钇矿和钇萤石是一种既富Y、Ln、F，又贫Na、Ca、CO2、P的介质的地球化学标志。
AbstractTveitite-(Y) as pods up to 10 cm across has been found at Mt. Rovgora, the Western Keivy, Kola Peninsula, Russia, in an albite-quartz-amazonite pegmatite vein related to alkaline granite. Tveitite-(Y) grains (up to 4 cm) are parallel microintergrowths of two isostructural varieties, Ca9.5Na1.7Y5.2Ln2.0F42.6 and Ca11.4Na1.9Y4.4Ln1.4F42.0. The idealized structural formula (Z = 3) is (Y, Na)6(Ca, LREE)6(Ca, Na, HREE)6(Ca, Na)F42; the simplified formula is (Ca, REE, Na)13(Y, Na)6F42; space group R$$
\bar 3
$$a = 17.020, c = 9.679 Å. [Lanthanoides are abbreviated in this paper as Ln, whereas Ln + Y as REE]. Nine fluorite samples containing from 0 to 18 mol % (REE)F3 were examined by electron microprobe, X-ray powder diffraction, and IR spectroscopy. The crystal structure of natural yttrofluorite has been determined for the first time (Raniso = 1.47 %): Fm3m, a = 5.493 Å; the structural formula is (Ca0.82Y0.12Ln0.06)F2.15. Earlier published and new data show that yttrofluorite containing (REE)F3 > 20 mol % and REE-enriched fluorite with LREE > Y (HREE) are metastable under room conditions. In nature, tveitite-(Y) is a product of solid-state transformation of metastable yttrofluorite with (REE)F3 > 20 mol %. Inferred protophases could have been exsolved into tveitite-(Y) variable in composition or tveitite-(Y) + yttrofluorite stable under normal conditions. The formation of tveitite-(Y) requires the erichment of a protophase not only in Y but also in LREE and HREE as stabilizing admixtures regularly distributed by different types of Ca-dominant structural sites. Tveitite-(Y) and yttrofluorite are geochemical indicators of a medium that is not only enriched in Y, Ln, and F, but also depleted in Na, Ca, CO2 and P.