Citation: Sokolova, E.; Hawthorne, F. C. (2013). From structure topology to chemical composition. XIV. Titanium silicates: refinement of the crystal structure and revision of the chemical formula of mosandrite, (Ca~3~REE)[(H~2~O)~2~Ca~0.5\\square 0.5~]Ti(Si~2~O~7~)2~(OH)~2~(H~2~O)~2~, a Group-I mineral from the Saga mine, Morje, Porsgrunn, Norway. Mineralogical Magazine, 77, pp. 2753-2771.