Two main types of silicification occur together: (1) voids partly or entirely filled with quartz, and (2) limestone matrix that has been replaced by microcrystalline quartz with preservation of most of the primary limestone fabric.There is a systematic relationship between silicification and high-porosity zones.However, the modeling shows that the kinetics of quartz precipitation limit the development of the silica replacement, whereas the diffusion of the dissolved species, from the replacement front towards the voids, seems to limit calcite dissolution.
These lacustrine limestones commonly contain cherts that crosscut sedimentary structures.
Observance began in 1993 and has grown significantly ever since; for the general public to show support, it is encouraged for the public to not use their taps throughout the whole day, the day has become a popular Facebook trend.
The basic objectives of carrying out of the World day of water resources: — To promote acceptance of corresponding measures for a solution of a problem of supply of the population potable water; — To inform the public on importance of protection and preservation of resources of fresh water and water resources as a whole; — To involve in celebrating of the World day of water resources of the government, the international agencies, the non-governmental organizations and a private sector.
Water scarcity is among the main problems to be faced by many societies and the World in the XXIst century.
Water use has been growing at more than twice the rate of population increase in the last century, and, although there is no global water scarcity as such, an increasing number of regions are chronically short of water.