Minerals in the rocks, which are then carried along in the water solution. The dissolving ability of the water is greater if chlorine or fluorine is present, because these elements react with many metals (such as copper) to form salts (copper chloride, for example) that are soluble in water. When the hot the Earth's crust, a chemical reaction between the metal salts and the sulfur produces metal sulfides. Because metal sulfides are not soluble in water, they form deposits by settling out of the dilution. Hydrothermal processes, are responsible for deposit-, of minerals such as gold, silver, copper, lead, and

The chemical and physical weathering pro­cesses that break rock into finer and finer particles in Chapter 14) but in the production of mineral deposits. Weathered particles can be transported by water and deposited as sediment on riverbanks, deltas. During their transport, certain minerals in the weathered particles dissolve in the water. They later settle out of solution—for example, when the warm water of a river meets the cold water of the ocean—because less material dissolves in cold water than in warm water. Important deposits of iron, manganese, phosphorus, sulfur, copper, and oilier minerals have been formed by sedimentation. During their transport, certain minerals in the weathered particles dissolve in water.

Significant amounts of dissolved material can accumulate in inland lakes and in seas that have no outlet or only a small outlet to the ocean. If these bodies of water dry up by evaporation, a large amount of salt is left behind; over time, it may be­come incorporated into rock layers. (There is geo­logical evidence that the Mediterranean Sea once dried up completely, for example. When water spilled back into the sea, its vast salt deposits were covered with sediment.) Significant worldwide deposits of common salt (NaCl), borax (Na2B₄O₇), potassium salts, and gypsum (CaSO₄-2H,O) Have been Formed by evaporation.