Abstract: Black and tawny cuticles are the most common colors among nephrite gravels. In this paper multi testing techniques including rock slip, electron probe, differential thermal analysis and so on were used to reveal colorcausing of the nephrite gravels. The testing results showed that limonite caused the tawny cuticle color and limonite with organic compound caused the black cuticle color, which offers evidence for identifying nephrite gravels and is also of significance in genetic research of nephrite gravels.