Abstract: In industrial diamonds synthesized using powder catalysts under high temperature and high pressure conditions， there is a small number of dark diamond particles. To explore the formation mechanism of dark industrial diamonds， Fe₇₀Ni₃₀ powder was used as the catalyst， high-purity graphite as the carbon source， and dolomite as the inner lining insulating material to synthesize industrial diamonds under high temperature and high pressure conditions. The morphology of the synthesized rod was characterized using optical microscopy and scanning electron microscopy. The outer region of the rod was subjected to acid washing and purification treatment to analyze its distribution. XRD was used to analyze the phase of the dolomite lining. The results show the overall proportion of dark industrial diamonds ranges from 1% to 2%， primarily distributed in the outer regions of the synthetic core columns. Their appearance exhibits pits and defective surfaces， with poor crystal morphology and numerous internal inclusion impurities. XRD analysis reveals that the dolomite liner decomposed into CaO and CO₂. Under high-temperature and high-pressure conditions， the CO₂ may react with the carbon source to form CO， which affects the diffusion between the catalyst and the carbon source. This process leads to the formation of more inclusion impurities， ultimately resulting in darker-colored diamonds.

Key words: industrial diamond; dark particle; high temperature and high pressure; powder catalyst; colour