High hardness and high crack resistance are usually mutually exclusive in glass materials. Through the aerodynamic levitation and laser melting technique, we prepared a series of magnesium aluminosilicate glasses with a constant MgO content, and found a striking enhancement of both hardness and crack resistance with increasing Al2O3. The crack resistance of the magnesium aluminosilicate glass is about five times higher than that of the binary alumina‐silica glass for the similar [Al]/([Al] + [Si]) molar ratio (around 0.6). For the selected magnesium aluminosilicate glass with R = 0.32, when subjected to isothermal treatment at 1283K, we observed a further drastic enhancement of both hardness and crack resistance by extending the heating time. Based on the structural analyses, we propose an atomic‐scale model to explain the mechanism of synergetic enhancement in hardness and crack resistance for the magnesium aluminosilicate glasses and glass‐ceramics.

By using the aerodynamic levitation and laser melting technique to well extend the glass‐forming region into the Mg‐rich and peraluminous regime, a series of magnesium aluminosilicate glasses were prepared to investigate the Mg and Al mixed effects on thermal properties, including glass transition temperature (Tg), crystallization behavior, and thermal stability. With the gradual substitution of Mg by Al, Tg exhibits two types of near‐linear rises with different slopes in two compositional regions separated by r = 0.57, where r is equal to the molar ratio of [Al2O3]/([Al2O3] + [MgO]). Moreover, when it comes to other properties, that is, crystallization behavior and thermal stability, this critical point precisely appears at the same r = 0.57. Compared to the slower increase of Tg in Mg‐rich region, the steeper rise of Tg in the peraluminous region is mainly ascribed to the step‐by‐step formation of oxygen triclusters driven by Pauling's second rule. Moreover, the occurrence of the critical point for Tg rise at r = 0.57 rather than the theoretical 0.5 can be seen as a proof of the role of Mg cations partly as a network former.