ZrN-Si3N4 composite powders were synthesised from natural zircon and quartz via carbothermal reduction and nitridation reaction. The effects of various raw material compositions and heating temperatures on phase transformation and product morphologies under flowing nitrogen atmosphere were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The phase equilibrium relationships of the ZrO2-SiO2-C-N-2 system at different heating temperatures were also investigated based on the thermodynamic analysis. Products with different phase compositions and morphologies were obtained at different conditions. The products were composed of ZrN, beta-Si3N4 and a small amount of c-ZrO2 by carbothermal reduction and nitridation of zircon with less than 20 wt.% quartz. With 30 wt.% quartz, granular ZrN as well as columnar and acicular beta-Si3N4 were detected in the products. With 40 wt.% or 50 wt.% quartz, the products consisted of ZrN, beta-Si3N4, Si2N2O, c-ZrO2 and m-ZrO2. The optimum quartz content for synthesizing ZrN-Si3N4 composite powders was 30 wt.%. At heating temperatures below 1600 degrees C, the products were composed of ZrN, beta-Si3N4, beta-SiC, Si2N2O, m-ZrO2 and c-ZrO2. (C) 2013 Elsevier B.V. All rights reserved.