Silicon-29 echo train coherence lifetimes and geminal 2J-couplings in network modified silicate glasses

•Residual dipolar couplings to alkali determine Si-29 coherence lifetimes in silicates.•Residual couplings to alkali make Si-29 lifetimes sensitive probes of structure.•Si-29 coherence lifetimes increase linearly with MAS speed and pi-pulse rate.•Distribution of Si-29 J couplings across Si-O-Si linkages obtained with PIETA.•J coupling distribution widths sensitive to silicate network disorder.