Although the content of Mg2+ in hard tissues is very low (typically ≤ 1.5 wt%), its incorporation into synthetic hydroxyapatite (HAp) particles and its role in the mineral's properties are still subject of intensive debate. A combined experimental-computational approach is used to answer many of the open questions. Mg2+-enriched HAp particles are prepared using different synthetic approaches and considering different concentrations of Mg2+ in the reaction medium. The composition, morphology and structure of the resulting particles are investigated using X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, scanning and transmission electron microscopies, FTIR, and wide-angle X-ray diffraction. After this scrutiny, the role of the Mg2+ in the first nucleation stages, before HAp formation, is investigated using atomistic molecular dynamics simulations. Saturated solutions are simulated with and without the presence of DNA, which has been recently used as a soft template in the biomineralization process. This synergistic investigation provides a complete picture of how Mg2+ ions affect the mineralization from the first stages onwards.