Abstract: A borosilicate glass, containing 25 wt. % of simulated high-level radioactive waste has been reacted with water at 350°C and 500 bars for 14 and 48 days using large-volume ‘cold-seal’ high-pressure equipment. Under these conditions the glass crystallizes a suite of mineral phases including: albite, NaAlSi₃O₈; aegirine, NaFeSi₂O₆; riebeckite, Na₂Fe₂(Fe,Mg)₃Si₈O₂₂(OH)₂; zektzerite, LiNaZrSi₆O₁₅; barium-strontium molybdate, (Ba,Sr)MoO₄; stillwellite, (Nd,Ce,La)BSiO₅; willemite, Zn₂SiO₄; smectite; a lithium-sodium borosilicate hydrate; melilite (åkermanite), Ca₂MgSi₂O₇. A description of the morphology of these phases is given, together with a number of chemical analyses. The implications of the incorporation of waste species in these mineral phases to the disposal of high-level radioactive waste is discussed.