Octahydrates are a type of hydrate that contain eight water molecules (H₂O) for each formula unit of the compound. They are often formed when certain salts or minerals crystallize from aqueous solutions, incorporating water into their structure. This additional water can influence the physical and chemical properties of the substance. Common examples of octahydrates include copper(II) sulfate octahydrate and magnesium sulfate octahydrate. These compounds are typically represented in chemical formulas with a dot notation, indicating the number of water molecules associated with the solid. Understanding octahydrates is important in fields like chemistry and materials science.