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Single crystals of Cu 2 ZnGeSe 4 and Cu 2 ZnGeS 4 solid solutions were developed and successfully obtained using the chemical vapor transfer method, with iodine acting as a transporter. The structure, compositional dependences of lattice parameters, pycnometric and X-ray densities and microhardness were determined. The chemical composition determined by the X-ray microanalysis satisfactorily corresponds to the nominal one with a tolerance of ±5 %. The XRD analysis showed that all the obtained compounds and their solid solutions have unit cell described by tetragonal symmetry. The attice parameters were found to be а  = 5.342 ± 0.005 Å, с  = 10.51 ± 0.01 Å for the Сu 2 ZnGeS 4 compound and а  = 5.607 ± 0.005 Å, с  = 11.04 ± 0.01 Å for the Cu 2 ZnGeSe 4 , respectively. Structural studies confirmed the validity of the Vegard's law in relation to the obtained samples. The pycnometric densities of ∼4.28 g/cm 3 for the Cu 2 ZnGeS 4 and ∼5.46 g/cm 3 for the Cu 2 ZnGeSe 4 were found to be slightly less than their X-ray densities of ∼4.32 g/cm 3 and ∼5.52 g/cm 3 , respectively. The maximum microhardness of ∼398 kg/mm 2 for these solid solutions corresponds to x  = 0.60. The melt point of the solid solutions increases from ∼1180 °C for the Сu 2 ZnGeSe 4 up to ∼1400 °C for the Сu 2 ZnGeS 4 . Based on X-ray fluorescence analysis and DTA data, the phase diagram of the Cu 2 ZnGeSe 4 -Cu 2 ZnGeS 4 system was constructed. Analysis of the obtained diagram indicates its first type according to Rozbom's classification., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)