赤铁矿(α-Fe₂O₃)和针铁矿(α-FeOOH)是风成沉积物和土壤中常见的两种致色矿物, 具有重要的环境指示意义。 赤铁矿指示干热环境条件, 针铁矿指示湿冷环境条件。 两者同存于沉积物或土壤中, 相互竞争。 在实际研究中, 通过应用两者的比例来指示环境条件的变化。 由于天然样品中赤铁矿和针铁矿含量低、 磁性弱, 传统的X射线衍射方法、 化学分析法以及岩石磁学方法都难以准确、 便捷地检测出二者的含量。 基于两者光学特征, 近年来越来越多的研究者使用漫反射光谱和色度方法尝试进行天然样品中赤铁矿和针铁矿的定量研究。 然而, 这两种方法也存在着一些问题。 漫反射光谱中赤铁矿和针铁矿特征峰强度受基底效应、 晶格离子替代等因素影响; 色度参数的红度同样受晶格离子替代影响, 黄度影响因素更为复杂。 因此, 两种方法的相关参数不能简单地等同于赤铁矿或针铁矿含量。 两种方法的对比研究显得尤为重要。 采用漫反射光谱和色度两种方法分别对干旱区的新疆博乐、 半湿润区的四川金川和湿润区的广东徐闻三个风成沉积剖面进行实验, 分析不同参数对于赤铁矿和针铁矿的指示意义及其适用范围。 在此基础上, 探讨针铁矿与赤铁矿比值的环境指示意义。 研究结果表明: (1)漫反射方法与色度方法是识别风成沉积物中针铁矿和赤铁矿信号的有效方法, 但由于影响因素复杂, 在大范围空间内仅能作为半定量指标; (2)a^*能够较好地指示赤铁矿含量, Gt/Hm与b^*/a^*能够较好地反映针铁矿与赤铁矿之间的比值, 但Gt与b^*不能很好地指示针铁矿的含量; (3)大气水热条件不能完全等同于土体水热条件。 大气降水并非完全进入土体, 温度通过蒸发作用影响土壤中水分含量, 土体水热状况受多因素影响。 大范围地理空间尺度上, 温度决定化学反应速率, 对于赤铁矿和针铁矿的生成与保存作用大于降水量。

Haematite (α-Fe₂O₃) and goethite (α-FeOOH) are two chromogenic minerals commonly found in aeolian sedimentsand soils. They are important indicators of environmental change. Haematite indicates dry and hot environmental conditions, while goethite indicates wet and cold environmental conditions. They compete with each other and coexist in sediments and soils. In practical research, the ratio of goethite to haematite is used to indicate changes in environmental conditions. Due to the low content and weak magnetism of haematite and goethite in natural samples, traditional methods, such as X-Ray diffraction, chemical analysis and rock magnetism, have difficulty accurately and conveniently detecting their contents. Based on their optical characteristics, an increasing number of researchers have tried to quantify haematite and goethite in natural samples using diffuse reflectance spectroscopy and chromaticity methods in recent years. There are some differences between these two approaches. The intensity of the characteristic peaks of haematite and goethite in the diffuse reflectance spectrum is affected by the substrate effect, lattice ion substitution and other factors. The redness (a^*) of the chromaticity parameter is also affected by lattice-ion substitution, and the factors affecting the yellowness (b^*) are more complicated. Therefore, the relevant parameters of the two methods cannot be simply equivalent to the content of haematite or goethite. It is particularly important to compare the two approaches. In this study, we use diffuse reflectance spectroscopy and chromaticity to conduct experiments on three aeolian sedimentary profiles: Bole, Xinjiang, in an arid region; Jinchuan, Sichuan, in a subhumid region; and Xuwen, Guangdong, in a humid region; to analyse the indicative significance and applicable range of different parameters for haematite and goethite and to discuss the environmental significances of the ratio of goethite to haematite. The results show that diffuse reflectance spectroscopy and chromaticity methods effectively identify the signals for goethite and haematite in aeolian sediments. However, due to the complex influencing factors, they can only be used as semiquantitative indicators in a large range of space. a^* can better indicate haematite content; Gt/Hm and b^*/a^* can also better reflect the ratio of goethite to haematite; but Gt and b^* cannot indicate well the content of goethite. Atmospheric hydrothermal conditions cannot be completely equal to soil hydrothermal conditions, atmospheric precipitation does not completely enter the soil, temperature affects the moisture content in the soil through evaporation, and the hydrothermal condition of the soil is affected by many factors. Temperature determines the rate of chemical reactions on a large geographic spatial scale, and the effect of temperature on the formation and preservation of haematite and goethite is greater than that of precipitation.