Hydratesare composed with water of crystallization in their structures.
When a hydrateis thermally exposed, it absorbs enormous quantity of heat (endothermic) andforms anhydrous mineral. When an anhydrate is immersed into water; it absorbswater and releases huge quantity of heat transforming into a hydrate mineral 6.In other way, it can be expressed that a hydrate is formed by releasingenormous quantity of heat from its anhydrous product. For an example; theformation snow from freezing water releases heat and snowfalls warms up theatmosphere may be cited. The heat released into the pore space might promotefurther evaporation of pore fluids.
Most of the hydrates are stable and solublein water at room temperature. Efflorescencemay cause spontaneous loss of water of crystallization in some hydrates. Othersabsorb water into their structure forming hydroscopic hydrates.
Deliquescentmineral like sodium hydroxide absorb huge quantities of water and form asliquid. The decomposition of carbohydrates generally releases water. Thus waterof crystallization in a hydrate minerals play critical role on their changes inspecific gravities and volumes 7. Hydration is not a reversible reaction;however, the environment crystallization of hydrates plays critical role forthe formation of hydrates and anhydrates 8. The repeated hydration and dehydration changes the volume of salineminerals which in turn affects the volume of pore spaces and hairline cracksare induced. Most pores are partially or completely filled with saline porefluids and repeated influxes of saline fluids and evaporations play criticalrole on the evolution of saline precipitates 9.
The evaporation of saline fluids precipitatessaline minerals initially at peripheral portions of saline droplets inside thepores. The ionic components of chloride, carbonate and sulphate, hydroxide andwater play critical role in the formation of mixed crystals of mineralcomponents rather than individual minerals. The scope of the investigationmainly lies to trace the trend of changes of chemical composition duringsuccessive crystallization of chloride components from the primary carbonatesource. Generally, the composition of groundwater is enriched with bicarbonatesand depleted in carbonates. Similar condition is true in the case of salinewaters interlocked in the pore spaces of lime-mortars.