硅硼镁铝矿复杂（高次）孪晶的微结构研究

本文用透射电子显微技术研究了硅硼镁铝矿的显微结构特征。研究结果表明:该矿物发育复杂(高次)生长孪晶,即(202)孪晶,(280)(202)二次孪晶,(04I)(280)(202)三次孪晶和(443)四次孪晶。并阐明了矿物高次孪晶的相互结构关系。同时,在TEM明场象中观察到了该矿物复杂孪晶对应的结晶形态。笔者还总结了低对称复杂孪晶显微结构的分析方法。

Microstructural Study of Complex High-Order Twin of Grandidierite

Grandidierite, a rare mineral with ideal chemical formula (Mg, Fe)AI_3SiBO_9 was discovered in 1987 in Jixi County, Heilongjiang Province. X-ray diffraction analysis and transmission electron microscopic study (TEM)of the mierostructure of grandidierite show that this mineral belongs to orthorhombic system with the unit cell parameters a=10.318(2), b=10.981(1), c=5.753(1) and the space group Pbnm.Microstructural analysis of the complex (high-order) twins is very complicated, Formerly, much study was devoted to simple high-order twins existent in metal materials and minerals, with less attention paid to the study of the complex (high-order) twins in the low symmetrical minerals. When studying the microstucture of grandidierite by means of TEM in our laboratory, we discovered for the first time complex (high-order) twins in the mineral and obtained the selected area electron diffraction (SAED) and the electron micrograph of the high-order twin.The SAED and the bright field image of TEM have been used jointly to determine the complex (high-order) twins in grandidierite, i.e., (202) growth twin, (280) (202) sec3ndary order twin, (041)(280)(202) third order twin, and (443) fourth order twin. The structural relationship between the complex (high-order) twins in the mineral has been illustrated, and the analytical method for the microstruetures of the minerals with low symmetry and complex (high-order) twins has been summarized.Experimental results show that there are splits of electron diffraction spots in four directions, i.e., along [202], [280]_T, [041]_(TF), [443], suggesting that there are plane defects on the crystallographic planes (202), (280)_T, (041)_(TF), (443) in the mineral. The discovery and study of the microstruetural characteristics of the low symmetrical and complex (high-order) twins in borate mineral have furnished new data to modern mineralogy.