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We have identified a convenient strategy for the control of the thermal growth of monoclinic Sr-anorthite and tialite phases in Sr–Ti–Al–silicates. The proposed method gives rise to a novel glassceramic material with thermal, mechanical, and dielectric properties potentially interesting in applications which require high temperature resistant radiotransparent materials. Crucially, we have found that the selective growth of Al2TiO5 and monoclinic SrAl2Si2O8 is enabled by keeping the SrO/Al2O3 ratio lower than unity. This strategy permits to prevent the crystallisation of detrimental rutile and hexagonal Sr-anorthite. Interestingly, the stable properties of monoclinic Sr-anorthite, never used in conjunction with tialite, give rise to a glassceramic system with good mechanical resistance (micro-hardness 9.6GPa, modulus of rupture 100MPa) and with relatively stable values of thermal expansion (49×10−7°C−1 from 20 to 1250°C), thermal diffusivity (0.45×10−6m2s−1), thermal conductivity (1.0W°C−1m−1), and dielectric constant (8.2) up to 1200°C.