Mineral reactions cement-rock

Published experimental studies of mineral/cal-cium hydroxide reactions show that at low temperatures (below 110°C), the chief reaction products are calcium silicate hydrate (CSH) gels, while zeolites and feldspars are formed at higher temperatures and in the presence of alkalis NaOH and KOH. The phase identifications have however often been made by low resolution or bulk methods, neither of which are ideal for such material. Published results of numerical simulations are in broad agreement with those of experimental studies of cement/ rock interaction. These models predict that CSH gels will be replaced by zeolites and maybe feldspars as plume chemistry evolves. 

In light of the small solubilities of many minerals, the extent of reaction predicted by this type of calculation may be smaller than expected. Considerable amounts of diagenetic cements are commonly observed, for example, in sedimentary rocks, and crystalline rocks can be highly altered by weathering or hydrothermal fluids. A titration model may predict that the proper cements or alteration products form, but explaining the quantities of these minerals observed in nature will probably require that the rock react repeatedly as its pore fluid is replaced. Local equilibrium models of this nature are described later in this section. 

Diagenesis is the set of processes by which sediments evolve after they are deposited and begin to be buried. Diagenesis includes physical effects such as compaction and the deformation of grains in the sediment (or sedimentary rock), as well as chemical reactions such as the dissolution of grains and the precipitation of minerals to form cements in the sediment s pore space. The chemical aspects of diagenesis are of special interest here. 

Chemical reactions between water and solids and the dissolution of cementing minerals may weaken the rock ... 

Action of water on rock over long periods of time typically leads to weathering and water erosion, physical processes that convert solid rocks and minerals into soil and sediment, but under some conditions chemical reactions with water occur as well, resulting in metasomatism or mineral hydration, a type of chemical alteration of a rock which produces clay minerals in nature and also occurs when Portland cement hardens. 

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