Abstract In Castanar Cave (Caceres, Spain), Mg-Si phases forming fibres and films occur associated with aragonite, magnesite, huntite and spheroidal dolomite in moonmilk, coatings and crust speleothems. A detailed study of bulk and carbonate-removed samples allowed us to identify the Mg-Si phases as kerolite (Mg3Si4O10(OH)2·nH2O) and sepiolite Mg4Si6O15(OH)2·6(H2O) of variable “crystallinity” and very pure composition. Under the scanning electron microscope, kerolite appears as gelatinous, smooth masses or films, showing some desiccation features. Sepiolite mostly occurs as isolated fibres 50 to 200 nm thick and up to 50 μm long and mats of interwoven fibres of several shapes. Analytical pyrolysis (Py-GC/MS) of the organic matter associated with these minerals in the moonmilk speleothems shows a compound assemblage lacking carbohydrates, nitrogen-bearing molecules and fatty acids, indicating no microbial activity. Kerolite and sepiolite most probably formed abiotically by direct precipitation in the cave waters, in conditions of high silica and magnesium activity and relatively high pH. These conditions were attained by local CO2 degassing taking place in extremely slow drips and capillary waters in speleothems with a large surface area, in a dynamic system where the renovation of infiltrated waters and diagenetic transformations of carbonates and silicates also contributed to significant hydrochemical variability at the microscale.

中文翻译：

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洞穴环境中与富镁碳酸盐伴生的陨石和海泡石的沉淀

摘要 在Castanar Cave（西班牙卡塞雷斯）中，形成纤维和薄膜的Mg-Si 相与文石、菱镁矿、辉长岩和球状白云岩一起出现在月乳、涂层和地壳洞穴中。对大块样品和去除碳酸盐的样品的详细研究使我们能够将 Mg-Si 相鉴定为具有可变“结晶度”且非常纯的岩橄榄石 (Mg3Si4O10(OH)2·nH2O) 和海泡石 Mg4Si6O15(OH)2·6(H2O)作品。在扫描电镜下，角纹石呈凝胶状、光滑的团块或薄膜，呈现出一定的干燥特征。海泡石主要以 50 至 200 nm 厚、长达 50 μm 的孤立纤维和多种形状的交织纤维垫形式出现。月奶洞穴中与这些矿物质相关的有机物的分析热解 (Py-GC/MS) 显示出一种缺乏碳水化合物的复合组合，含氮分子和脂肪酸，表明没有微生物活动。Kerolite 和海泡石很可能是通过在洞穴水中的直接沉淀，在高二氧化硅和镁活性以及相对高 pH 值的条件下非生物形成的。这些条件是通过在具有大表面积的洞穴中极慢的滴水和毛细管水中发生的局部 CO2 脱气来实现的，在一个动态系统中，渗透水的更新和碳酸盐和硅酸盐的成岩转变也有助于显着的水化学变化。微量。