Phosphonates are commonly used in industry for scale prevention in a wide variety of water systems. In many of these applications, the phosphonates are able to react with divalent cations such as calcium to form stable divalent cation-phosphonate precipitates. The focus of this paper is to identify and study how different precipitating factors will affect the resulting properties of calcium-phosphonate precipitates and to show how the formation of different precipitates can be used to enhance scale treatments in oil field applications. The phosphonate used in this study was 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). The three precipitating conditions under study were (1) the pH of the precipitating solution, (2) the calcium/ HEDP molar ratio of the precipitating solution, and (3) the degree of supersaturation of the precipitating solution. The results in this paper showed that while the degree of supersaturation had a minimal effect on the resulting precipitate properties, the coupled effects of pH and calcium/HEDP molar ratio had a significant effect on the resulting precipitate properties. At the extreme conditions, two distinct precipitates were synthesized : one comprised of fibrous spindles having a calcium/HEDP molar ratio of 1:1 and the other comprised of spherical particles having a calcium/HEDP molar ratio of 2:1. Finally, micromodel experiments were carried out to test the performance of these two distinct precipitates with respect to phosphonate treatments in petroleum production systems. The results showed that the slow dissolution of the spherical particles and the morphology of the fibrous spindles were highly advantageous in slowing the phosphonate release from a porous medium, ensuring successful phosphonate treatments in oil field applications.