Silicon (Si) influences the biologic activity of calcium phosphate materials by modifying material properties and by direct effects on the physiological processes in skeletal tissue. Compositions belonging to the system dicalcium silicate (Ca2SiO4 = C2S)-tricalcium phosphate (Ca3(PO4)2 = TCP), able to release that element in situ, are promising candidates for preparing new ceramic bone implants. An exact knowledge of the phase relationships in the system is required to design materials with controlled phase compositions and properties. Thus, a study of the sub-system a-TCPss-Silicocarnotite within the C2STCP system was studied as a preliminary step toward obtaining new monophasic and/or biphasic bioceramics. Phase composition of the resulting ceramics was studied using X-ray diffraction and scanning electron microscopy with attached wavelength dispersive spectrometer. The results showed that the sub-system presents an invariant eutectoid point at 1158 degrees C +/- 2 degrees C for a composition of 83 wt% Ca3(PO4)2 and 17 wt% Ca2SiO4, and typical eutectoid microstructure of lamellae morphology.