This paper analyses the mineralogical composition, texture, and structure of a stalactite sampled from the city-wall storerooms of the Nueva Tabarca fortress (southeast Spain). This speleothem presents an uncommon mineral assemblage: aragonite, brucite, gypsum, silica, and halite. Internally, it shows complex structure: (1) a central soda-straw composed by aragonite; (2) an external puff-pastry cone-crust formed preferentially by aragonite and brucite; and (3) an internal branching of coralloids, showing a subtle layering between brucite and aragonite. Gypsum, halite, and silica locate in the outer coating of the cone-crust. The sequent mineral precipitation sequence has been established: aragonite > brucite > gypsum/silica > halite. Speleothem formation is directly related to the chemical weathering of the rocks and mortars used as building materials of the city-wall. Brucite precipitates has been always linked to the presence of MgO-based geomaterials. However, the lack of these compounds as building materials in Nueva Tabarca fortress makes this investigation a unique example of brucite precipitation. PHREEQC calculations showed that interaction between pore waters and the minerals of mortar aggregates (dolomite, pyroxene, and amphibole) leads to rich-magnesium solutions. Evaporation modelling of lixiviated waters describes the precipitation of the mineral assemblage of the brucite-aragonite speleothems.

中文翻译：

---

水镁石文石沉淀物是历史性的非基于MgO的土工材料的风化产物

本文分析了从Nueva Tabarca堡垒（西班牙东南部）的城墙储藏室采集的钟乳石的矿物学组成，质地和结构。蛇纹石具有不常见的矿物组合：文石，水镁石，石膏，二氧化硅和石盐。从内部看，它显示出复杂的结构：（1）由文石组成的中央苏打秸秆；（2）由文石和水镁石优先形成的外部粉扑-锥壳。（3）珊瑚的内部分支，在水镁石和文石之间显示出微妙的分层。石膏，盐石和二氧化硅位于锥壳的外涂层中。已经确定了随后的矿物沉淀顺序：文石>水镁石>石膏/二氧化硅>岩盐。蛇纹石的形成与用作城墙建筑材料的岩石和砂浆的化学风化直接相关。水镁石沉淀物一直与基于MgO的土工材料有关。但是，由于在Nueva Tabarca堡垒中缺少这些化合物作为建材，这项研究成为水镁石沉淀的独特例子。PHREEQC计算表明，孔隙水与砂浆团聚体的矿物（白云石，辉石和闪石）之间的相互作用导致了富镁溶液。浸没水的蒸发模型描述了水镁石-文石蛇麻石矿物组合的沉淀。Nueva Tabarca堡垒中缺少这些化合物作为建筑材料，使该研究成为水镁石沉淀的独特例子。PHREEQC计算表明，孔隙水与砂浆团聚体的矿物（白云石，辉石和闪石）之间的相互作用导致了富镁溶液。浸没水的蒸发模型描述了水镁石-文石蛇麻石矿物组合的沉淀。Nueva Tabarca堡垒中缺少这些化合物作为建筑材料，使该研究成为水镁石沉淀的独特例子。PHREEQC计算表明，孔隙水与砂浆骨料矿物（白云石，辉石和闪石）之间的相互作用会导致富镁溶液的产生。浸没水的蒸发模型描述了水镁石-文石蛇麻岩矿物组合的沉淀。