VO and VO2 vanadyl groups with short (typically 1.57–1.68 Å), essentially covalent, V—O bonds are common for V4+‐bearing oxysalts with 5‐ and 6‐coordinated vanadium. There is a clear negative correlation between vanadyl bond lengths and wavenumbers of the bands of V—O stretching vibrations in infrared spectra (in the range 1000–880 cm−1). Optical, structural and chemical data for vanadyl minerals are used to calculate Gladstone–Dale compatibility coefficients. Gladstone–Dale compatibility indices of minerals containing vanadyl bonds are compared with total electronic polarizabilities of V4+. Unlike compounds of 5‐coordinated Ti4+, for most minerals with V4+=O (vanadyl) bonds there is good agreement between measured refractive indices and those calculated based on the polarizability concept. There is a clear negative correlation between the vanadyl bond lengths and wavenumbers of the bands of V—O stretching vibrations in infrared spectra. For most minerals with vanadyl bonds there is good agreement between measured refractive indices and those calculated based on the polarizability concept.