Hematite is a canted antiferromagnet with reddish color that occurs widely on Earth and Mars. Identification and quantification of hematite is conveniently achieved through its magnetic and color properties. Hematite characteristics and content are indispensable ingredients in studies of the iron cycle, paleoenvironmental evolution, paleogeographic reconstructions, and comparative planetology (e.g., Mars). However, the existing magnetic and color reflectance property framework for hematite is based largely on stoichiometric hematite and tends to neglect the effects of cation substitution, which occurs widely in natural hematite and influences the physical properties of hematite. Thus, magnetic parameters for stoichiometric hematite are insufficient for complete analysis of many natural hematite occurrences and can lead to ambiguous geological interpretations. Remagnetization, which occurs pervasively in red beds, is another ticklish problem involving hematite. Understanding red bed remagnetization requires investigation of hematite's formation and remanence recording mechanisms. We elaborate on the influence of cation substitution on the magnetic and color spectral properties of hematite, and on identifying hematite and quantifying its content in soils and sediments. Studies of remagnetization mechanisms are discussed, and we summarize methods to discriminate between primary and secondary remanences carried by hematite in natural samples to aid primary remanence extraction in partially remagnetized red beds. Although there remain unknown properties and unresolved issues that require future work, recognition of the properties of cation-substituted hematite and remagnetization mechanisms for hematite will aid identification and interpretation of the magnetic signals that it carries, which is environmentally important and responsible for magnetic signals on Earth and Mars.

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赤铁矿的磁性和颜色反射特性：从地球到火星

赤铁矿是一种倾斜的反铁磁体，呈红色，广泛存在于地球和火星上。通过赤铁矿的磁性和颜色特性可以方便地识别和量化赤铁矿。赤铁矿的特征和含量是铁循环、古环境演化、古地理重建和比较行星学（如火星）研究中不可缺少的成分。然而，现有赤铁矿的磁性和颜色反射特性框架主要基于化学计量赤铁矿，往往忽略了阳离子取代的影响，阳离子取代广泛存在于天然赤铁矿中，影响赤铁矿的物理性质。因此，化学计量赤铁矿的磁参数不足以完整分析许多天然赤铁矿矿点，并可能导致地质解释不明确。在红层中普遍发生的再磁化是另一个涉及赤铁矿的棘手问题。了解红床再磁化需要研究赤铁矿的形成和剩磁记录机制。我们详细阐述了阳离子取代对赤铁矿的磁性和颜色光谱特性的影响，以及识别赤铁矿并量化其在土壤和沉积物中的含量。讨论了再磁化机制的研究，我们总结了区分天然样品中赤铁矿携带的初级和次级剩磁的方法，以帮助在部分再磁化的红层中提取初级剩磁。