The transformation behavior between iron oxides and oxyhydroxides like magnetite, hematite and goethite is still not entirely understood. Crystallographic similarities allow one to predict topotactic relationships between them. The related crystallographic aspects have been explored by means of electron backscatter diffraction (EBSD). Samples from natural aggregates of magnetite, hematite and goethite were collected from iron‐formation rocks that outcrop in the southeast of Brazil, in a region known for large deposits of iron and other ores. EBSD misorientation data indicate a pronounced relationship between these iron phases. The transformation seems to be related to the oxygen framework. The original close‐packed cubic arrangement of O atoms in magnetite changes to a hexagonal close‐packed framework in hematite, i.e. {111} of magnetite is parallel to {0001} of hematite. The matrix in which the magnetite grains are embedded is made of aggregates of hematite and goethite. In the matrix, the coincidence observed in the magnetite grains is not observed. On the other hand, the well known twin boundary relationships already described for these mineral phases can be observed here as an orientation relationship in three‐dimensional misorientation space. The spatial data of axis–angle pairs suggest that the twin boundaries serve as facilitating surfaces for phase transformation in the Fe–O–OH system. The main conclusion of this study is that the transformation occurred in the solid state with the newly transformed goethite inheriting the crystallographic orientations of the former crystals and that this phenomenon is better recognized by combining observations of misorientation relationships. In the matrix, such a relation is not observed and, for that reason, the minerals in the matrix are thought to have been formed by a different process, which might have involved dissolution and precipitation of the phase newly out of solution.

中文翻译：

---

针铁矿，赤铁矿和磁铁矿中的取向不良关系：以巴西铁四方铁矿中的铁形成岩为例

仍未完全了解铁氧化物和羟基氧化物（如磁铁矿，赤铁矿和针铁矿）之间的转变行为。晶体学相似性使人们可以预测它们之间的电位关系。已经通过电子背散射衍射（EBSD）探索了相关的晶体学方面。来自磁铁矿，赤铁矿和针铁矿的天然聚集体的样品是从巴西东南部露头的铁矿岩中采集的，该地区以铁和其他矿石的大量沉积而闻名。EBSD取向不良数据表明这些铁相之间存在明显的关系。该转变似乎与氧骨架有关。磁铁矿中O原子的原始密堆积立方排列变为赤铁矿中的六角密堆积骨架，即磁铁矿的{111}与赤铁矿的{0001}平行。嵌入磁铁矿晶粒的基质由赤铁矿和针铁矿的聚集体组成。在基体中，未观察到在磁铁矿晶粒中观察到的一致。另一方面，已经在这些矿物相中描述的众所周知的孪晶边界关系可以在这里观察为三维错位空间中的方向关系。轴角对的空间数据表明，孪晶边界可作为Fe–O–OH系统中相变的促进面。这项研究的主要结论是，相变是在固态下发生的，新相变的针铁矿继承了以前晶体的晶体学取向，并且结合了取向差关系的观察结果可以更好地识别这种现象。在基体中，没有观察到这种关系，因此，认为基体中的矿物是通过不同的过程形成的，这可能涉及新的相从溶液中溶解和沉淀出来。