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Some sedimentary rocks and minerals consist of chemicals that had been once dissolved in water.

Certain limestones formed this way. Oolitic limestone consists of billions of oolites: tiny balls produced by calcium carbonate accumulating on particles rolled around by gentle currents in warm, shallow seas. Oolite forms like this today on the Bahama Banks. Dolomitic limestone (limestone mainly made of the mineral dolomite) occurs where certain brines chemically alter preexisting limestone or where dolomite deposits form in an evaporating sea.

Such so-called evaporites underlie one-quarter of the continents in beds up to 4,000 ft (1220 m) thick. Evaporites form now where chemical deposits accumulate in evaporating desert takes and coastal salt flats. But certain old evaporites could have been precipitated from chemically oversaturated deep offshore waters of almost landlocked seas such as the Mediterranean.

Three main minerals tend to settle in a sequence. First comes calcium carbonate. Next is gypsum (a granular crystalline form of calcium sulfate combined with water. Then comes sodium chloride in the form of halite (rock salt.) This is a soft, low density rock and liable to flow. Pressure from overlying rock forces up huge plugs / domes of salt beneath the coast of Texas and Louisiana and in parts of Germany, Iran and Russia.

Besides the rocks and minerals just named, there are other chemical deposits. A few have or had important economic uses – particularly borax, chert and flint; certain iron-rich compounds, nitrates and phosphorites. But some of these are partly biological in origin; and scientists disagree about how certain forms of iron occurred.

(David Lambert “The Field Guide to Geology” 1988, Cambridge University Press)