The bulk (volume) crystallisation of Li2O . 2SiO(2) (LS2) glasses with additions of 1, 2 and 5 mol % P2O5 (G1P, G2P and G5P) was investigated. In the G1P and G2P glasses heated at 454 degrees C metastable alpha'- and beta'-LS2 crystal phases formed initially and only stable LS2 at later stages. In G1P heated at 463 degrees C transmission electron microscopy (TEM) revealed particles (greater than or equal to 2 mu m) of stable LS2 but also smaller (< 0.1 mu m) crystalline particles which were unstable under the electron beam and could not be identified. Crystalline lithium orthophosphate (Li3PO4) was detected by XRD and P-31 magic angle spinning nuclear magnetic resonance (MAS-NMR) in both as-quenched and heat treated G5P but not in G1P and G2P. In G5P heated at 476 degrees C, metastable alpha'-LS2 phase initially formed and at later times stable LS2. In as-quenched G5P, a trace of lithium metasilicate (LS) was observed. Li3PO4 crystals were not detected in G5P by TEM but a marked increase in nucleation rate due to P2O5 addition was observed. Si-29 MAS-NMR revealed amorphous Q(2) (LS) and Q(4) (SiO2) species in an average Q(3) (LS2) environment in the as-quenched glasses. Increased P2O5 concentration caused a greater degree of amorphous phase separation. (3)1P MAS-NMR showed amorphous lithium phosphate units in the as-quenched and nucleated G1P and G2P. The presence of crystalline Li3PO4 phase in glass G5P suggests that Li3PO4 crystals may act as sites for heterogeneous nucleation of stable lithium disilicate.