Limestone can be dissolved by water and therefore may develop karst features, such as enlarged rock joints or caves. Sedimentary deposits made up of common table salt and impurities, formed after water evaporated from ancient seas. Salt is plastic-like, flexing in all three dimensions under enough pressure. It therefore does not fracture. Shale usually acts as a barrier to groundwater movement, but in some situations may serve as an aquifer whose water moves primarily through the horizontal layers.
Siltstones vary in chemical composition.
Siltstones vary in their degree of hardness and may act as aquifers. Rock produced from ash and rock fragments that have been ejected by violent volcanic eruptions. Some particles may partially re-melt by the residual volcanic heat, thus forming a welded tuff. Fracturing of rock resulting in parallel displacement relative to each side along the fault zone. Faults easily act as conduits for groundwater.