calcium ion than a magnesium ion to shed its hydration shell and bind to a growing crystal. It is also more difficult to nucleate a seed crystal of ordered dolomite than disordered high-magnesium calcite. As a result, attempts to precipitate dolomite from seawater precipitate high-magnesium calcite instead. This substance, which has an excess of calcium over magnesium and lacks calcium-magnesium ordering, is sometimes called protodolomite. Raising the temperature makes it easier for magnesium to shed its hydration shell, and dolomite can be precipitated from seawater at temperatures in excess of . Protodolomite also rapidly converts to dolomite at temperatures of or higher. It is possible that microorganisms are capable of precipitating primary dolomite. This was first demonstrated in samples collected at Lagoa Vermelha, Brazil in association with sulfate-reducing bacteria (Desulfovibrio), leading to the hypothesis that sulfate ion inhibits dolomite nucleation. Later laboratory experiments suggest bacteria can precipitate dolomite independently of the sulfate concentration. With time other pathways of interaction between microbial activity and dolomite formation have been added to the discored regarding their role in modulation and generation of polysaccharides, manganese and zinc within the porewater. Meanwhile, a contrary view held by other researchers is that microorganisms precipitate only high-magnesium calcite but leave open the question of whether this can lead to precipitation of dolomite. Dedolomitization Dolomitization can sometimes be reversed, and a dolomite bed converted back to limestone. This is indicated by a texture of pseudomorphs of mineral dolomite that have been replaced with calcite. Dedolomitized limestone is typically associated with gypsum or oxidized pyrite, and dedolomitization is thought to occur at very shallow depths through infiltration of surface water with a very high ratio of calcium to magnesium. Uses Dolomite is used for many of the same purposes as limestone, including as construction aggregate; in agriculture to neutralize soil acidity and supply calcium and magnesium; as a source of carbon dioxide; as dimension stone; as a filler in fertilizers and other products; as a flux in metallurgy; and in glass manufacturing. It cannot substitute for limestone in chemical processes that require a high-calcium limestone, such as manufacture of sodium carbonate. Dolomite is used for production of magnesium chemicals, such as Epsom salt, and is used as a magnesium supplement. It is also used in the manufacture of refractory materials. Caves in dolomite rock As with limestone caves, natural caves and solution tubes typically form in dolomite rock as