The XRD and FTIR of aragonites in nacreous and prismatic layer of perna viridis were systematically measured,and the frequency variations of ν₁,ν₂ and ν₄ band of aragonites were especially analyzed.The results showed that both of them were aragonite and the frequency of ν₂ band differed in them,but the frequencies of other two bands were not altered and had the same values with cavernous aragonite.In the same specie of shell,the frequency of ν₂ band in nacreous layers was greater than that in prismatic layers,and there was a frequency shift of ν₂ band between them.For the first time,the phase transformation of biogenic aragonite was detected.After nacreous aragonite was heated at 300 ℃,the frequency shift of ν₂ band was found.So it is concluded that the biogenic aragonite is related to the thermal effects in crystallizing process,meanwhile it stores excess energy.All of these can provide experiential basis for studying biomineralization theory.