Yes, under the appropriate pH conditions and alkalinity, iron and calcium may precipitate together, with the iron precipitating as ferrous (Fe++) hydroxide and the calcium as a carbonate. This combined precipitation forms gnarled tubercules around anodic areas on pipes. When the Fe++ hydroxide dissolves away pits are left in the metal. Also, depending on carbonate concentration and whether oxygen is absent, Fe++ may precipitate as FeCO3 (siderite), sometimes as a layer in conjunction with calcium carbonate. The most common iron precipitate in water where oxygen is present however is ferric (Fe+++) hydroxide, since it is sparingly soluble in waters with pH values above 5, while ferrous (Fe++) hydroxide is much more soluble. In the presence of oxygen, ferrous hydroxide is readily oxidized to ferric hydroxide. Through dehydration, 2 molecules of ferric hydroxide may loose three molecules of water to form ferric oxide, which has the more familiar red color of rust.