Nitrogen-rich Ca–α-SiAlON ceramics with nominal compositions CaxSi12−2xAl2xN16 and 0.2≤x≤2.6, extending along the Si3N4–1/2Ca3N2:3AlN tie line, were prepared from Si3N4, AlN, and CaH2 precursors by hot pressing at 1800°C. The x values attained were determined by energy-dispersive X-ray (EDX) microanalysis and X-ray powder diffraction (XRPD) data using the Rietveld method. The results show that Ca–α-SiAlONs form continuously within the compositional range x=0 to at least x=1.82. Phase assemblages, lattice parameters, Vickers hardness, and fracture toughness were determined and correlated to the calcium content, x. Owing to a high sintering temperature and the use of CaH2 as a precursor, grain growth was kinetically enhanced, resulting in self-reinforced microstructures with elongated grains. The obtained Ca–α-SiAlON ceramics demonstrate a combination of both high hardness ∼21 GPa, and high fracture toughness ∼5.5 MPa·m1/2.