The long-known presence of a sharp OH absorption band in the tetragonal fluoride mineral sellaite, MgF₂, inspired us to conduct a detailed study of the OH incorporation modes into this IR-transparent (where IR stands for Infrared) material as well as to search for hydrogen traces in two other IR-translucent halides—villiaumite (NaF) and fluorite (CaF₂). Among these three phases, sellaite is the only one to incorporate ‘intrinsic’ OH groups, most commonly as O–H∙∙∙F defects oriented nearly perpendicular to the c-axis along the shortest edge of the constituent MgF₆ polyhedra, in analogy with the isostructural mineral rutile, TiO₂. Another defect type, seen only scarcely in untreated natural material, develops when subjecting sellaite to temperatures above 900 °C. It involves an O–H∙∙∙O cluster along the 2.802 Å edge of the original MgF₆ dipyramid, as fluorine atoms are progressively expelled from the structure, being replaced by O^2- anions. This is corroborated by the appearance of spectral absorption features typical for brucite (Mg(OH)₂) and ultimately periclase (MgO), the presence of which could be proven via powder diffraction of the heat-treated material. Except for a ‘dubious’ peak most probably caused by included phases, neither villiaumite (NaF) nor fluorite (CaF₂) showed any presence of ‘intrinsic’ OH defects. They do however decompose along a similar route into the respective oxide and hydroxide phases at high temperature. This thermal decomposition of the studied halide phases is accompanied by the emission of gaseous (HF)_n species at temperatures well below their established melting point - a subject which seems to be quite overlooked.

四方氟化物矿物硅镁石 MgF ₂中存在尖锐的 OH 吸收带这一众所周知的事实启发我们对这种 IR 透明（IR 代表红外线）材料中的 OH 掺入模式进行了详细研究，以及在另外两种红外半透明卤化物——钒铝石 (NaF) 和萤石 (CaF ₂ )中寻找氢痕迹。在这三个相中，镁铝石是唯一包含“固有”OH 基团的相，最常见的是 O–H∙∙∙F 缺陷，其取向几乎垂直于沿构成 MgF ₆多面体最短边的c轴，以此类推与同构矿物金红石，TiO ₂. 另一种缺陷类型在未经处理的天然材料中很少见，当镁铝石经受 900 °C 以上的温度时会出现这种缺陷。它涉及沿原始 MgF _{6双锥的 2.802 Å 边缘的 O–H∙∙∙O 簇，因为氟原子逐渐从结构中排出，被 O} ^2-阴离子取代。_{水镁石 (Mg(OH) 2} ) 和最终方镁石 (MgO)典型的光谱吸收特征的出现证实了这一点，其存在可以通过热处理材料的粉末衍射来证明。除了很可能由内含物相引起的“可疑”峰外，无论是钒铅矿 (NaF) 还是萤石 (CaF ₂) 表明存在任何“固有”OH 缺陷。然而，它们确实会在高温下沿着类似的途径分解成相应的氧化物和氢氧化物相。所研究的卤化物相的这种热分解伴随着气态 (HF) _n物种在远低于其既定熔点的温度下的排放——这一主题似乎被完全忽视了。