Figure 22 shows the dependence of (a) the hardness measured in nanoindentation experiments using a Berkovich diamond tip, (b) N_{NBO}/N_T, (c) N_{NBO}/[N_{Mg} + N_{Al_mcc}], and (d) the mean Al-O coordination number n_{Al}^{O}  on the mol% of silica for glasses on or near to the tectosilicate tie-line.