Crystal-chemical and carbon-isotopic characteristics of karpatite (C24H12) from the Picacho Peak Area, San Benito County, California:: Evidences for the hydrothermal formation
Crystal-chemical and carbon-isotopic characteristics of karpatite (C24H12) from the Picacho Peak Area, San Benito County, California:: Evidences for the hydrothermal formation
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DOI：
10.2138/am.2007.2509
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发表时间：
2007-08-01
影响因子：
3.1
通讯作者：
Maruoka, Teruyuki
中科院分区：
文献类型：
--
作者：
Echigo, Takuya;Kimara, Mitsuyoshi;Maruoka, Teruyuki
加州圣贝尼托县Picacho峰地区的Karpatite经红外吸收分析、拉曼散射分析和差热分析鉴定为一种异常纯净的冠烯(C24H12)晶体。此外，还首次用单晶X射线衍射法测定了钙钛矿的晶体结构。该矿物属单斜晶系，空间群P2(1)/a，晶胞参数a=110.79(9)，b=4.690(3)，c=10.049(8)埃，β=110.79(2)度，V=709.9(8)埃(3)，Z=2。卡帕特晶体结构中的冠烯分子都是孤立的，分子间距离符合范德华相互作用。冠烯分子具有高度的芳香性，没有过度拥挤的氢原子，这两者都避免了其他多环芳烃(PAHs)在卡帕特中的混合。组成方解石的冠烯分子的波纹排列防止了插层反应，这是这种矿物具有特殊纯度的原因。现今卡帕特岩的C-13值为-22.39+/-0.18%(O)(vs.VPDB)，与遥远构造区沉积有机质的碳同位素组成相似。这种有机质可能被热液转化为冠烯分子，从而形成卡帕特石。结构关系表明，在热液中强烈聚集冠烯分子后，卡帕特石的生长发生在热液石英沉淀和随后的朱砂形成之后。
Karpatite from the Picacho Peak Area, San Benito County, California, has been characterized as an exceptionally pure crystal of coronene (C24H12) by infrared absorption analysis, Raman scattering analysis, and differential thermal analysis. Furthermore, the crystal structure of karpatite was determined using a single-crystal X-ray diffraction method for the first time. The mineral crystallizes in the monoclinic system, space group P2(1)/a, with unit-cell dimensions of a = 16.094(9), b = 4.690(3), c = 10.049(8) angstrom, beta = 110.79(2)degrees, V = 709.9(8) angstrom(3), and Z = 2. The structure was solved and finally refined to R-1 = 3.44% and wR(2) = 2.65%, respectively. The coronene molecules in the crystal structure of karpatite are all isolated and the intermolecular distances correspond to van der Waals interactions. The coronene molecules have the high degree of aromaticity and no overcrowded hydrogen atoms, both of which avoid a mixing of other polycyclic aromatic hydrocarbons (PAHs) in karpatite. The corrugated arrangement of coronene molecules constituting karpatite prevents intercalation reactions, accounting for the exceptional purity of this mineral.The isotopic composition of carbon was measured, using an elemental analyzer-isotopic ratio mass spectrometer (EA/IRMS). The present karpatite yielded a delta C-13 value of -22.39 +/- 0.18%(o) (vs. VPDB), which is similar to carbon isotopic compositions of sedimentary organic matter in the far-reaching tectonic regions. This organic matter might be converted to coronene molecules by hydrothermal fluids leading to formation of karpatite. Textural relationships indicate that after the strong concentration of coronene molecules in hydrothermal fluids, karpatite growth postdates both hydrothermal quartz precipitation, and subsequent cinnabar formation.