Nano-particles of calcium and phosphorous compounds are made in a highly pure generally amorphous state by spray drying a weak acid solution of said compound and evaporating the liquid from the atomized spray in a heated column followed by collection of the precipitated particles. Hydroxyapatite (HA) particles formed by such apparatus and methods are examples of particle manufacture useful in bone and dental therapies. Dual nozzle spraying techniques are utilized for generally insoluble compounds.