crystals containing molecules of water.
Many salts, acids, and bases are precipitated from aqueous solutions in the form of crystal hydrates. Many naturally occurring minerals, such as gypsum (CaSC4·2H2O) and carnallite (MgCl2·KCl·6H2O), are examples of typical crystal hydrates. The water of crystallization can usually be removed by heating. This is often accompanied by the stepwise decomposition of the crystal hydrate. For example, blue vitriol CuSO4·5H2O (dark blue) is converted to CuSO4·3H2O (light blue) and CuSO4·H2O (white) at temperatures above 105°C, and its complete dehydration takes place above 250°C. However, certain compounds (for example, BeC2C2O4·H2O) are stable only as crystal hydrates and cannot undergo dehydration without decomposing.