Micro- and nano-inclusions embedded in calcite phantom crystals from Gemerská Ves, Slovak Republic, have been characterized by a combination of Raman spectroscopy, scanning and transmission electron microscopy, X-ray powder diffraction, and C and O isotope analysis. Whereas the outer, colorless part of the phantom crystal is relatively homogeneous and cavity and inclusion-free, the inner terracotta-colored part contains abundant cavities, dolomite, hematite, goethite, titanite, phyllosilicates (mainly kaolinite and illite), and apatite inclusions and nanostructures that have formed on the walls of cavities. The nanostructures comprise hematite and goethite particles sandwiched between either two phyllosilicate crystals or a phyllosilicate and a carbonate (calcite or dolomite) crystal. Our observations suggest that all inclusions in the terracotta calcite originate from the terra rossa (a common soil type in karstic areas) and limestone outcropping adjacent to the calcite crystals. While the micrometer-sized phyllosilicate and hematite particles were likely transported from the terra rossa and attached to the surface of growing calcite, the presence of phyllosilicates that are only a few atomic layers thick and of euhedral hematite, goethite, and dolomite crystals suggests that these particles precipitated along with the phantom calcite in situ, from an aqueous solution carrying terra rossa-derived and limestone-derived solutes. The compositional differences between the terra rossa (e.g., smectite as the only major Mg-rich phase) and terracotta calcite inclusions (e.g., dolomite as the only major Mg-rich phase and the presence of only Mg-free clays) hint that a smectite-illite conversion provides the Mg necessary for the precipitation of dolomite and possibly the Fe associated with the iron oxyhydroxide nanostructures. Phyllosilicate nucleation on calcite and dolomite nucleation on phyllosilicates, as inferred from nanoscale mineralogical associations, suggest that carbonates and phyllosilicates may mutually enhance nucleation and growth. This enhancement may result in the formation of large-scale clay-carbonate successions in aqueous settings, including the enigmatic, pink-colored cap dolostones succeeding late Neoproterozoic “Snowball Earth” deposits. The distribution of inclusions in the terracotta calcite and the preferred nucleation of hematite and goethite on phyllosilicate, rather than on carbonate surfaces, indicates that phyllosilicates have a potential to not only disrupt crystal growth and trigger the formation of cavities in the structure of the calcite host, but also to provide surfaces for the precipitation of different phases in the cavities and to uniformly distribute otherwise incompatible materials in a calcite host crystal. This calls for further exploration of the potential application of phyllosilicates in composite structure development.

中文翻译：

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方解石幻晶中的包裹体表明粘土矿物在白云石形成中的作用

来自斯洛伐克共和国 Gemerská Ves 的方解石幻像晶体中嵌入的微米和纳米夹杂物已通过拉曼光谱、扫描和透射电子显微镜、X 射线粉末衍射以及 C 和 O 同位素分析的组合进行了表征。幻晶的外部无色部分相对均匀，无空洞和夹杂物，而内部赤土色部分则含有丰富的空洞、白云石、赤铁矿、针铁矿、榍石、页硅酸盐（主要是高岭石和伊利石）、磷灰石夹杂物和在空腔壁上形成的纳米结构。纳米结构包括夹在两个页硅酸盐晶体或一个页硅酸盐和一个碳酸盐（方解石或白云石）晶体之间的赤铁矿和针铁矿颗粒。我们的观察表明，赤土方解石中的所有包裹体都来自赤土（岩溶地区常见的土壤类型）和靠近方解石晶体的石灰岩露头。虽然微米级的页硅酸盐和赤铁矿颗粒很可能从红土中运出并附着在生长的方解石表面，但只有几个原子层厚的页硅酸盐和自面体赤铁矿、针铁矿和白云石晶体的存在表明这些颗粒与幻影方解石一起从携带红土衍生和石灰石衍生溶质的水溶液中原位沉淀。赤土（例如，绿土作为唯一的主要富镁相）和赤土方解石包裹体（例如，白云石作为唯一的主要富镁相和仅存在无镁粘土）暗示绿土-伊利石转化提供了白云石沉淀所必需的镁以及可能与羟基氧化铁纳米结构相关的铁。方解石上的层状硅酸盐成核和层状硅酸盐上的白云石成核，从纳米级矿物学关联推断，表明碳酸盐和层状硅酸盐可以相互促进成核和生长。这种增强可能导致在水环境中形成大规模的粘土-碳酸盐岩层序，包括继新元古代晚期“雪球地球”沉积物之后的神秘的粉红色盖层白云岩。赤土方解石中包裹体的分布以及层状硅酸盐上赤铁矿和针铁矿的优选形核，而不是在碳酸盐表面，表明页硅酸盐不仅有可能破坏晶体生长并引发方解石主体结构中空腔的形成，而且还可以为空腔中不同相的沉淀提供表面并均匀分布方解石主体晶体中的其他不相容材料。这需要进一步探索层状硅酸盐在复合结构开发中的潜在应用。