Polymorphs have different stabilities and may spontaneously convert from a metastable form (unstable form) to the stable form at a particular temperature. Most polymorphs of organic molecules only differ by a few kJ/mol in lattice energy. Approximately 50% of known polymorph pairs differ by less than 2 kJ/mol and stability differences of more than 10 kJ/mol are rare.[4] They also exhibit different melting points, solubilities (which affect the dissolution rate of drug and consequently its bioavailability in the body), X-ray crystal and diffraction patterns.