Irradiation with 200 keV electrons induced amorphism in natural beryl and cordierite, at fluences of ∼ 1026e/m2, a factor of ≈ 10 times that required to produce a similar effect in quartz. After dehydration of the beryl and cordierite by heating at 1050°C, the fluence required to induce amorphism was increased to ∼ 1027e/m2. The electron fluence required to produce amorphism in both materials decreased with decreasing electron energy, as expected if solid-phase radiolysis is responsible. CsAlSi5O12, prepared by dry-firing ceramic techniques, was rendered amorphous at a fluence of 3 × 1024e/m2(E= 200 keV). However, there was little apparent dependence of the electron fluence required to produce amorphism on electron energy over the 50–200 keV range, and Cs+migration may play a critical role in the crystalline ← amorphous transformation. A natural sphene was unaffected structurally by irradiation to a fluence of 2 × 1027e/m2(E= 200 keV). The data are consistent with established theories that open structures are prone to radiation-induced amorphism and that impurity electron- or hole-trapping centres augment the solid-phase radiolysis of silicates.