The removal of these ions from solution in water can be accomplished in two ways: either as the result of inorganic chemical processes, mainly evaporation and precipitation, or by living organisms. 

During precipitation, the materials are removed from the water; whereas during evaporation, the water is removed and the chemicals are left. The former might be caused by a change in temperature. For example, calcium carbonate, the chemical which makes up calcite, all other conditions being equal, is much more soluble in cold than in warm water. If water laden with this material is heated up, all of the dissolved material cannot remain in solution; and some of it settles out as a solid. In areas which have hard water, such as Florida, carbonates will precipitate out in water heaters, irons, and kettles, forming a deposit called scale. This same process operates on a geologic scale, where cold ocean waters saturated with lime and phosphate heat up in coastal areas and precipitate extensive deposits of limestones and phosphates. Consequently, the tropical and subtropical regions of the world are characterized by limestone deposition. 

Precipitation can also be caused by changes in acidity (pH). Secondary deposition of flint and chert or iron oxides and hydroxides, for instance, is related to pH changes. Inorganic precipitation usually involves materials which are near their saturation point, where small changes in surrounding conditions can cause the water to become saturated and thereby initiate precipitation. 

Materials that are not near saturation, such as sodium chloride, can only be removed by evaporating the water. The thick layers of rock salt and gypsum which underlie the Gulf Coast and the Mediterranean were formed when large portions of these seas evaporated. Overall, because of the preponderance of calcium released by weathering, the most common chemical sedimentary rock is limestone, followed by gypsum and rock salt. 

The second way in which ions can be removed from water is by the action of living organisms. Most marine organisms secrete tests (shells) of calcium carbonate or silica which they extract from sea water. After these organisms die, their shells accumulate to form layers of organic limestones and cherts. Although almost everyone is familiar with the shells which one finds on the beach, fewer people know that the white limestones of Alabama or the cliffs of Dover along the Channel in England and France are also formed from chalk, a limestone made from the accumulated remains of microscopic organisms. 

One other organic sedimentary rock, coal, is also important. Coal, rich in carbon, is formed from the remains of fossilized plants. It is one of the very few sedimentary rocks which is not directly derived from weathering. The carbon which makes it up the coal was originally extracted from the atmosphere by plants. This sedimentary source of fossil fuel is again achieving increased importance as petroleum resources dwindle. Originally mainly used as fuel, it has become a raw material base for the modern chemical industry. Unfortunately, because it contains some sulfur, the use of coal as an energy source has also generated enormous volumes of sulfur oxide emissions. These airborne pollutants are responsible for a significant part of our problems with acid precipitation.