皖北灵璧磬云石的岩石学和地球化学研究

Petrography and geochemistry of Lingbi Qingyun stone in northern Anhui Province

磬云石是产于灵璧地区震旦系张渠组地层中的一种微晶灰岩,以其色黑致密且敲击能发出青铜质的声音,而成为观赏名石和制作敲打乐器。磬云石主要矿物组成为微晶方解石,晶体自形程度较好,粒度均小于10μm,紧密镶嵌排列,富含有机质。在元素地球化学特征上,磬云石含有高的CaO含量,低的MgO、SiO2、Fe2O3、Al2O3含量,低的稀土元素含量,富集Sr、Cu、Mn、Ba等元素。通过与该套震旦系地层中产出的其他微晶灰岩对比研究表明,磬云石的矿物组成单一,颗粒大小均匀,颗粒排列紧密,颗粒间孔洞小且少,含有较高的有机质含量等特征,是其敲击能发出青铜质声音的主要原因。磬云石的形成与震旦纪时全球高的CO2浓度以及该区多发的地质事件有关,是震旦纪海水过饱和CaCO3的沉积环境与该区复杂的地质事件联合作用的结果。

Qingyun stone of Lingbi County is a type of microcrystalline limestone lying in Sinian Zhangqu Formation,characterized by black color,dense texture and bronze-like sound.It can be used as an ornament or musical instrument.The rock is dominated by euhedral microcrystalline calcite,up to 10 μm in size,with abundant organic matter.It has high CaO and low MgO,SiO2,Fe2O3,Al2O3,shows low REE concentrations,and is enriched in Sr,Cu,Mn and Ba.Based on a comparison of the petrographic and geochemical features between the Qingyun stone and the common microcrystalline limestone in the study area,the authors hold that the characteristics of the bronze-like sound produced by the Qingyun stone can be attributed to its single mineral assemblage,uniform grain size,dense texture,very small pore size and high organic matter abundance.The Qingyun stone was genetically associated with the global high CO2 concentrations and regional extraordinary geological events in Sinian period,being the combined result of the CaCO3 oversaturated sedimentary environments and the complex geological events.