YIN Ke1, HONG Han-lie1, WU Yu2 , HAN Wen1, HU Bai-zhong3, TU Cai3
(1 . Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China;
2. National Gemstone Testing Centre, Beijing 100013, China;
3. Institute of Jewellery, China University of Geosciences, Wuhan 430074, China)
Abstract: 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 of nanometer needle stone may result from microbial activity.
Key words: stone needle; mineralogy; genesis; coloration; nanometer; microbe
E-mail: yinke1984@qq.com
ACTA MINERALOGICA SINICA Vol. 33, No. 1, 2013, Page 38-44
