一种纳米粒级砭石的矿物学特征与成因

A Study on Mineralogy and Genesis of a Nanometer Stone Needle

为探究一种灰黑色砭石的矿物学特征及成因,采用X射线粉晶衍射(XRD)、扫描电子显微镜(SEM)、热重-微商热重分析(TG-DTG)及激光诱导离解光谱(LIBS)等分析方法对其矿物组成、结构特征、热力学性质及化学成分进行分析。结果表明,灰黑色砭石主要组成矿物为方解石(>98%),并含有少量石英、云母、长石、黄铁矿及微量石墨(<2%)。晶面尺寸测试及SEM分析结果显示,以上矿物单晶粒径大多处于纳米级别,砭石中矿物主要以块状、棒状及片状等3种集合体形式存在。微晶石墨呈分散态赋存在砭石中是灰黑色砭石致色的主要原因,而石英、云母、长石、黄铁矿及石墨等杂质的存在、纳米级的结构特征和类质同象导致砭石中方解石的热解温度远低于标准的纯方解石。砭石中纳米级方解石微球粒及石墨和黄铁矿微晶的存在,说明纳米级灰黑色砭石的形成可能与微生物的活动密切相关。

Mineral assemblages, structural characteristics, thermo-dynamic properties and chemical components were investigated using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, derivative thermogravimetric analysis （DTG）, and laser induced breakdown spectroscopy （LIBS） to understand the mineralogy and genesis of a nanometer stone needle. XRD and DTG results show that the black stone needle is mainly composed of calcite （〉98%）, with minor quarts, mica, feldspar, pyrite, and trace graphite （〈2%）. Average size and SEM analyses indicate that minerals from black needle stone are mostly in nanometer scopes and occur as mineral aggregate of massive and rod-like and flaky shapes. The coloration might result from an average distribution of graphite in the stone needle, and the occurrence of foreign minerals such as quarts, mica, feldspar, pyrite, and graphite and nanometer structure and isomorphism lead to the lower decomposition temperature of calcite than its standard equivalent. The occurrence of spherical nanometer calcite and microcrystal graphite and pyrite suggests that the formation ofnanometer needle stone may result from microbial activity.