Chemical sedimentary rocks

Sedimentary rocks formed from sediments created by inorganic processes are discussed below  

Class Rock name Texture Mineral composition Description 

1 Oolitic limestone Clastic Rounded calcite ooliths bounded by a calcite cement. Can be slightly dolomitized. 

5/5 3 O Q Travertin or siliceous tuff Calcedoine, jasper Amorphous Glassy Silica Rocks made from 50 wt.% sihca precipitaed from saturated aqueous solutions or metasomatic reaction. Diatomite are made from accumulation of siliceous skeletons of microorganisms. 

1 s- 1 Potash Crystalline Halite, sylvite, and carnallite Halite with sylvite, interlocking cubic crystals, sometimes contains orange-to-red carnallite crystals. 

05 3 O t-i t-i CIh Ironstone, taconite Crystalline Siderite, goethite, limonite  

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Metamorphic rock is the product of solid state process such as crystallization due to heat and pressure. The rock is generally left unchanged chemically. Sedimentary rocks are formed from pre-existing rocks by a number of processes known as denudation. Denudation consists of weathering, transportation and erosion. 

Tufa 1) A chemical sedimentary rock composed of calcium carbonate, which form in nonmarine settings. 2) Any snbaerial travertine deposit formed near a spring mouth, along a stream, in a marsh or lake. The term often refers to thin, porous, or soft deposits, as opposed to travertine used for massive, hard, dense deposits. 

Chemical sedimentary rocks form when highly soluble ions, such as Na Ca"% Mg % Cl , F, (S04> (COj) and (P04), from existing rocks are dissolved in water and subsequently precipitate forming layers in oceans and lakes where they become cemented together. The composition of sedimentary rocks depends on the... 

Briefly, sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks (1) clastic sedimentary rocks, such as breccia, conglomerate, sandstone, and shale, which are formed from mechanical weathering debris, (2) chemical sedimentary rocks, such as rock salt and some limestone rocks, which form when dissolved materials precipitate from solution, and (3) organic sedimentary rocks, such as coal and some limestone rocks, which form from the accumulation of plant or animal debris. 

Iron ore is a chemical sedimentary rock that forms when iron and oxygen (and sometimes other substances) combine in solntion and deposit as a sediment. Hematite is the most common sedimentary iron ore mineral. Rock salt (halite) is also a chemical sedimentary rock that forms from the evaporation of ocean or saline lake. It is rarely fonnd at Earth s snrface, except in areas of very arid climate and is often mined for use in the chemical indnstry or for nse as a winter highway treatment. Limestone is a rock that is composed primarily of calcinm carbonate. It can form organically from the accumulation of shell, coral, algal, and fecal debris. It can also form chemically from the precipitation of calcinm carbonate from lake or ocean water. 

Sedimentary rocks are classified depending on how they were formed. They are divided into four groups (a) clastic sedimentary rocks , (b) biochemical (or biogenic) sedimentary rocks, (c) chemical sedimentary rocks and (d) other sedimentary rocks formed by impact, volcanism and other processes. 

Chemical sedimentary rocks are formed as precipitates from supersaturated solutions precipitating out around. Oolitic limestone is an example of rock in this category. 

During chemical weathering, rocks and primary minerals become transformed to solutes and sods, and eventually to sediments and sedimentary... 

The most stable minerals are often physically eroded before they have a chance to chemically decompose. Minerals that decompose contribute to the dissolved load in rivers, and their solid chemical-weathering products contribute to the secondary minerals in the solid load. The secondary minerals and the more stable primary minerals are the most important constituents of clastic sedimentary rocks. Consequently, the secondary minerals of one cycle of erosion are... 

During the last two decades, many experimental studies on the seawater-rock interaction at elevated temperatures (100-400°C) have been conducted. Particularly, detailed seawater-basalt interaction experiments have been done. Several experimental studies on seawater-rhyolite interaction and seawater-sedimentary rock interaction are also available (Bischoff et al., 1981). Examples of chemical compositions of modified seawater experimentally interacted with various kinds of rocks are shown in Table 1.9. 

Many Cu-Pb-Zn vein-type deposits are hosted by organic sedimentary rocks such as shale and mud.stone but almost all Au-Ag deposits occur in altered volcanic rocks. This difference in the host rocks affects the chemical features of ore fluids (/02. /s2> /CO2) (section 1.4.4). 

Thick sedimentary pile from middle Miocene to late Pliocene is exposed in the Oga Peninsula, northern Honshu, Japan (Fig. 1.153). Age of the sedimentary rocks has been determined by microfossil data. Thus, the sedimentary rocks in the Oga Peninsula where type localities of Miocene sedimentary rocks in northern Japan are well exposed have been studied to elucidate the paleoenvironmental change of the Japan Sea (Watanabe et al., 1994a,b). Kimura (1998) obtained geochemical features of these rocks (isotopic and chemical compositions) and found that regional tectonics (uplift of Himalayan and Tibetan region) affect paleo-oceanic environment (oxidation-reduction condition, biogenic productivity). However, in their studies, no detailed discussions on the causes for the intensity and periodicity of hydrothermal activity, and temporal relationship between hydrothermal activity, volcanism and tectonics in the Japan Sea area were discussed. They considered only the time range from ca. 14 Ma to ca. 5 Ma. 

Kimura, S., (1998) Paleoceanographic Environment of Japan Sea Deduced from Chemical and Isotopic Features of Miocene-Pliocene Sedimentary Rocks. Doctoral Thesis, Keio University, 224 pp. 

Sedimentary rocks have formed as a result of accumulation and compaction of mineral particles derived from pre-existing rocks, transported from their original places of occurrence and deposited in new environments. The essential ingredients for the formation of sedimentary rocks are (i) source materials, (ii) mechanical and chemical disintegration of these source materials, (iii) transportation of the released materials either in a clastic form... 

The sedimentary rocks are classified on the basis of their mineral, chemical and particulate characteristics. Some common sedimentary rocks are conglomerate, sandstone, shale and limestone. 

Syn-sedimentary chemical deposits form by chemical and biochemical precipitation of valuable metal components carried in solution, concomitant with the formation of the enclosing sedimentary rock. The manner of such deposition depends on the concentration of the metal in the solvent, the solubility of the precipitating product, the solution chemistry, and the deposition environment. Iron, manganese, phosphorus, lead, zinc, sulfur and uranium are some of the elements that have formed economically valuable deposits by chemical precipitation during sedimentation. 

Historically, the alkali industry is based on limestone, or chalk. The chemical name for limestone is calcium carbonate (CaCOs). It is a very common mineral in seashells. Therefore, limestone is a naturally occurring sedimentary rock formed when seas or lakes evaporate. When limestone is heated, it produces carbon dioxide... 

The early period of the Earth s history, around 3.8 1 billion years ago, is completely shrouded in darkness possible witnesses from this archaic period might help to cast some light. So we are looking for possible remains of the first primitive life forms on our planet—fossils, or to be exact, microfossils, which refers to the remains of living cells. What have survived are mainly only cell walls, which can be isolated from sedimentary rocks when the silicate-, sulphide- or carbonate-rich minerals are chemically dissolved away. The microfossils are found in the remaining carbon-containing residue, transparently thin platelets of which are prepared for microscopic studies. 

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. 

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