Three different crystallographic modifications of mineral brianite were prepared from the melt. The temperatures of modification changes determined by DTA were 760 and 900 deg C, respectively. The interaction of all modifications with simulated body fluid (SBF) and with distilled water was studied. Hydroxy apatite was identified on the sample surfaces after the interaction of brianite with SBF using X-ray diffraction and X-ray micro analysis suggesting possible bioactivity. The time dependence of amount of brianite components in the solution can be described using equation NLi=Bi/Ki[1-exp(Kit)]+Wit. Considering general composition of precipitated layer CaxMg(10-x)(PO4)6(OH)2, the rate of dissolution and the rate of precipitation were estimated from Wi parameters using iteration method
