Abstract: Novel magnesiosilicate compounds for use in detergent compositions and as water softeners have a calcium binding capacity of at least 10 mg CaO per gram, a magnesium binding capacity of at least 10 mg MgO per gram and a calcium binding rate of no more than 300 seconds, all at room temperature. The compounds have a stuffed silica polymorph-related structure or a layered structure with a broad X-ray powder diffraction peak at a d-spacing of between 11 and 17 .ANG.. The compounds have an anhydrous composition M.sub.a Mg.sub.b Al.sub.c Si.sub.1-(b+c) O.sub.d, where M--alkali, 0.0<a<2.0, 0.0<b<0.7, 0.0.ltoreq.c.ltoreq.0.3, 1.15<d<3.0, c<b, and partial substitution of M, Mg, Al and Si is permitted.