Weathering also releases dissolved chemical elements into the streams and groundwater. Most of this invisible material is carried to the ocean.
Various natural processes, some inorganic, some biological, find ways to turn these dissolved chemicals back into sediment.
In terms of sheer volume, the most important of these chemical sediments is a chalky substance called calcium carbonate. Calcium carbonate is the precursor to lime, calcium oxide, which we use in cement, concrete, stucco, and many chemical processes.
Sea water is very nearly saturated in calcium carbonate, and in warm shallow seas made alkaline by flourishing marine life, it comes out of solution to form a pale-colored mud. Lime-secreting algae stiffen their leaves with calcium carbonate, which is released as tiny particles when they decay. Corals and shellfish build rigid homes out of calcium carbonate, contributing sand-sized particles when they die and their skeletons disintegrate.
By this endless living and dying, great banks and reefs of lime sediment can accumulate in warm, clear, shallow seas. These carbonate muds and sands are soon cemented into the third most common sedimentary rock, limestone.
The marine environment of this limestone is clearly revealed by the fossils of invertebrate sea creatures that it contains:
What all these sediments have in common is a relatively simple and pure chemical composition. In creating these sediments, nature has done nearly all the work of refining crustal material into substances man can use.