Abstract Warkite (IMA 2013-129) is a new Sc-rich ultrarefractory mineral in the rhonite group of the sapphirine supergroup. It has a P 1 ¯ aenigmatite-type structure with a = 10.367 A, b = 10.756 A, c = 8.895 A, α = 106°, β = 96°, γ = 125°, and Z = 2, and general formula of Ca2(Sc,Ti,Al,Mg,Zr)6Al6O20. Warkite occurs as micrometer-sized crystals in eleven ultrarefractory Ca,Al-rich inclusions (UR CAIs) from the CM, CV, CO, and CH chondrites. In the CM, CO, and CV CAIs, warkite in the cores coexists with a Ti-rich oxide, either perovskite or kangite; the cores are generally mantled and rimmed by davisite and/or Sc-diopside. In the CH CAIs and one CO CAI, warkite in the cores coexists with perovskite and grossite; the cores are mantled by grossite ± gehlenite, and rimmed by low-Sc, Al-diopside. Therefore, there are two basic families of warkite-bearing inclusions, those containing Sc-rich clinopyroxene but no grossite and those containing grossite but no Sc-rich clinopyroxene. Scandian clinopyroxene in warkite-bearing CAIs generally formed by the reaction of warkite, which supplied most or all of the Sc, Ti, and Al, and a nebular gas that supplied much of the Ca and O and virtually all of the Mg and Si. The presence of Sc-rich clinopyroxenes may reflect exposure of some warkite-bearing CAIs to a dust-rich environment, which would enhance partial pressures of Si-, Mg-, and Ca-bearing species in the vapor and make it oxidizing relative to a dust-poor gas. Warkite in grossite-bearing inclusions is generally Ti3+-enriched relative to those in davisite-bearing inclusions, consistent with their formation in relatively dust-poor, more-reducing environments. Warkite compositions are sensitive to the presence or absence of spinel, melilite, Sc-rich clinopyroxenes, and grossite. Compositional variations of perovskite and warkite grains indicate a connection but, except for late-stage Fe exchange, they did not equilibrate with each other. The presence of at least two trends in Y-Sc among perovskites without corresponding trends in warkite suggests that at least some perovskite formed separately. Warkite-bearing CAIs from CM2s and CO3.0s are uniformly 16O-rich (Δ17O ∼ −23‰), whereas those from metamorphosed COs and CVs are isotopically heterogeneous: warkite, kangite, perovskite, melilite, and davisite are 16O-depleted to various degrees (Δ17O range from −22 to −2‰) relative to hibonite, spinel, and forsterite, all having 16O-rich compositions (Δ17O ∼ − 25 to −20‰). We infer that warkite-bearing CAIs originated in an 16O-rich nebular gas. Subsequently, CAIs from metamorphosed CVs and COs experienced O-isotope exchange with an 16O-depleted external reservoir, most likely aqueous fluids on the CV and CO chondrite parent asteroids; however, O-isotope exchange in the solar nebula cannot be excluded.

中文翻译：

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Warkite，Ca2Sc6Al6O20，一种碳质球粒陨石中的新矿物和太阳星云超难熔包裹体中的基石相

摘要 Warkite (IMA 2013-129) 是一种新的富钪超难熔矿物，位于蓝宝石超群的菱镁矿群中。它有一个 P 1 ¯ 玄武岩型结构，a = 10.367 A, b = 10.756 A, c = 8.895 A, α = 106°, β = 96°, γ = 125°, Z = 2, 通式为Ca2(Sc,Ti,Al,Mg,Zr)6Al6O20。Warkite 以微米级晶体的形式出现在来自 CM、CV、CO 和 CH 球粒陨石的 11 种超难熔 Ca、Al 富集包裹体 (UR CAIs) 中。在 CM、CO 和 CV CAI 中，核中的钙钛矿与富钛氧化物共存，钙钛矿或康钛矿；岩心通常被英石和/或Sc-透辉石覆盖和包围。在CH CAI和一个CO CAI中，核中的钙钛矿与钙钛矿和钙钛矿共存；核心被毛长石±黄长石覆盖，边缘被低钪铝透辉石包围。所以，有两种基本的含镁辉石的包裹体，一类含有富钪单斜辉石但不含粗斜辉石，一类含粗斜辉石但不含富钪单斜辉石。含钙钛矿的 CAI 中的斯堪的单斜辉石通常由供应大部分或全部 Sc、Ti 和 Al 的warkite 与提供大部分 Ca 和 O 以及几乎所有 Mg 和 Si 的星云气体反应形成。富含 Sc 的单斜辉石的存在可能反映了一些含钙钛矿的 CAIs 暴露在富含灰尘的环境中，这会增加蒸汽中含硅、镁和钙的物质的分压，并使其相对于含尘气体。与含晶石包裹体中的那些相比，含毛铁矿包裹体中的 Warkite 通常富含 Ti3+，这与它们在相对贫尘的环境中的形成一致，更多还原环境。Warkite 成分对尖晶石、黄长石、富含 Sc 的单斜辉石和粗长石的存在与否很敏感。钙钛矿和钙钛矿晶粒的成分变化表明存在联系，但除了后期 Fe 交换外，它们并没有相互平衡。钙钛矿中 Y-Sc 中至少存在两种​​趋势，而钙钛矿中没有相应的趋势，这表明至少有一些钙钛矿是单独形成的。来自 CM2s 和 CO3.0s 的含 Warkite 的 CAI 均富含 16O（Δ17O ∼ -23‰），而来自变质 COs 和 CVs 的 CAIs 是同​​位素异质的：warkite、康石、钙钛矿、黄长石和菱镁矿的 16O 贫化到各种度（Δ17O 范围从 -22 到 -2‰）相对于黑曜石、尖晶石和镁橄榄石，均具有富含 16O 的成分（Δ17O ∼ - 25 到 -20‰）。我们推断，含石英的 CAI 起源于富含 16O 的星云气体。随后，来自变质 CV 和 CO 的 CAI 经历了与 16O 耗尽的外部储层的 O 同位素交换，很可能是 CV 和 CO 球粒陨石母小行星上的含水流体；然而，不能排除太阳星云中的氧同位素交换。