The object is the invention is to provide hollow and preferably porous spherical CaP particles preferably without the use of strontium ions. This is achieved by a method comprising the steps: a) Providing an aqueous buffer solution of purified water having a pH of 6 10 comprising 20 200 mM sodium ions 0.1 10 mM potassium ions and 1 10 mM phosphate ions and wherein the buffer solution is essentially free from strontium b) adding calcium ions in the range of from 0.1 to less than 2mM and magnesium ions in the range of 0.01 5 mM to the buffer solution and forming a mixture c) heating the mixture of step b) at 60 200 °C for at least 5 minutes d) isolating the formed particles and e)optionally washing the isolated particles using a suitable solvent. The particles comprise 40 70 weight% of calcium 20 40 weight% of phosphate and 1 25 weight% magnesium. The Ca/P weight ratio is in the range of 1.10 to 1.90 and more than 80 % of the particles have a particle size between 200 to 1500 nm. The particles are essentially free from strontium. A composition comprising the particles may be used for remineralization of teeth or as bone void filling material.
