Chemical composition of nyerereite and gregoryite from natrocarbonatites of Oldoinyo Lengai volcano, Tanzania
Chemical composition of nyerereite and gregoryite from natrocarbonatites of Oldoinyo Lengai volcano, Tanzania
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坦桑尼亚 Oldoinyo Lengai 火山的钠碳酸盐岩中的尼雷石和砾石的化学成分
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发表时间：
2009
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通讯作者：
V. Sharygin
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作者：
A. Zaitsev;J. Keller;J. Spratt;T. Jeffries;V. Sharygin
坦桑尼亚北方Oldoinyo Lengai火山碳酸盐岩熔岩中的主要矿物为碱金属碳酸盐Nyerereite（理想的Na 2Ca（CO 3）2）和钙铝榴石（理想的Na 2CO 3）。它们以斑晶和微斑晶的形式出现在由萤石和钾盐组成的基质中; Nyerereite通常形成棱柱状晶体，而钙铝榴石则以圆形、椭圆形晶体出现。这两种矿物的特点是各种微量元素含量相对较高。拉曼光谱数据表明硫和磷以（SO 4）2-和（PO 4）3-基团的形式存在。微探针分析表明，变量组合物的Nyerereite和钙铝榴石。尼雷尔矿含有6.1- 8.7wt%的K 2 O，以及少量的SrO（1.7- 3.3wt%）、BaO（0.3- 1.6wt%）、SO 3（0.8- 1.5wt%）、P 2 O 5（0.2- 0.8wt%）和Cl（0.1- 0.35wt%）。钙铝榴石含有5.0-11.9重量%的CaO、3.4-5.8重量%的SO 3、1.3-4.6重量%的P 2 O 5、0.6-1.0重量%的SrO、0.1-0.6重量%的BaO和0.3-0.7重量%的Cl。氟的含量低于检测限的Nyerereite和钙铝榴石。激光烧蚀ICP-MS分析表明，稀土、锰、镁、铷、锂等元素是这些矿物中的典型微量元素。尼雷尔矿富含稀土元素（高达1080 ppm）和Rb（高达140 ppm），而镁铝榴石则比尼雷尔矿含有更多的镁（高达367 ppm）和锂（高达241 ppm）。
Alkali carbonates nyerereite, ideally Na2Ca(CO3)2 and gregoryite, ideally Na2CO3, are the major minerals in natrocarbonatite lavas from Oldoinyo Lengai volcano, northern Tanzania. They occur as pheno- and microphenocrysts in groundmass consisting of fluorite and sylvite; nyerereite typically forms prismatic crystals and gregoryite occurs as round, oval crystals. Both minerals are characterized by relatively high contents of various minor elements. Raman spectroscopy data indicate the presence of sulfur and phosphorous as (SO4)2− and (PO4)3− groups. Microprobe analyses show variable composition of both nyerereite and gregoryite. Nyerereite contains 6.1–8.7 wt % K2O, with subordinate amounts of SrO (1.7–3.3 wt %), BaO (0.3–1.6 wt %), SO3 (0.8–1.5 wt %), P2O5 (0.2–0.8 wt %) and Cl (0.1–0.35 wt %). Gregoryite contains 5.0–11.9 wt % CaO, 3.4–5.8 wt % SO3, 1.3–4.6 wt % P2O5, 0.6–1.0 wt % SrO, 0.1–0.6 wt % BaO and 0.3–0.7 wt % Cl. The content of F is below detection limits in nyerereite and gregoryite. Laser ablation ICP-MS analyses show that REE, Mn, Mg, Rb and Li are typical trace elements in these minerals. Nyerereite is enriched in REE (up to 1080 ppm) and Rb (up to 140 ppm), while gregoryite contains more Mg (up to 367 ppm) and Li (up to 241 ppm) as compared with nyerereite.