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 2 mM, 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.
