Calcitic mudstone

Calcitic mudstone is cemented ealeitie mud (micrite), with few coarse grains. 

In this case study, the selected phases are pyrite, amorphous FeS, calcite (present in limestones in the roof strata Fig. 5), dolomite (possibly also present in the limestones), siderite (which occurs as nodules in roof-strata mudstones), ankerite (present on coal cleats in the Shilbottle Seam), melanterite and potassium-jarosite (representing the hydroxysulphate minerals see Table 3), amorphous ferric hydroxide (i.e., the ochre commonly observed in these workings, forming by precipitation from ferruginous mine waters), and gypsum (a mineral known to precipitate subaqueously from mine waters with SO4 contents in excess of about 2500 mg/L at ambient groundwater temperatures in this region, and with which most of the mine waters in the district are known to be in equilibrium). In addition, sorption reactions were included in some of the simulations, to contribute to the mole transfer balances for Ca, Na, and Fe. 

Shales are very fine-grained sedimentary rocks consisting of 67 % or more clay-sized (<4 pm) particles. Unlike mudstones, siltstones, and claystones, shales are very laminar and fissile that is, they readily split into thin, closely spaced, and parallel layers (Boggs, 1995), 181. Along with clay minerals, shales may have abundant microscopic quartz, feldspars, pyrite, hematite, calcite, dolomite, and/or organic matter (Boggs, 1995), 178. 

D 6.43 Laminated mudstone Quartz, mica-illite, calcite Plagioclase, montmoril-lonite( )... 

Unlike calcite and dolomite, siderite rarely forms as an extensive pore-filling cement, but rather as discrete fine crystals, spherules and nodules scattered in the host sediments. Nevertheless, Baker et al. (1996) found that early diagenetic siderite concretions (0.5-2 mm) form up to 30% of Triassic sandstones and mudstones from eastern Australia. Laterally continuous siderite-cemented offshore shelf sandstone sheets (15 cm thick) occur in Upper Cretaceous sequences from Canada (McKay et ai, 1995). 

Decrease in COj induced when fluids migrate to high permeability, underpressured lithologies, such as at interface between mudstones and sandstones, or along fault zones that are connected to underpressured zones. The precipitation of calcite can thus be envisaged as follows ... 

In addition to cement, microcrystalline calcite occurs as laminae in lacustrine sediments that often reveal evidence of disruption, presumably due to desiccation shrinkage during periodic exposure. Fibrous calcite similar to radiaxial cements which occur in ancient limestones commonly occurs as vugular void fillings in these microcrystalline calcite laminae. Similar microcrystalline calcite is in some cases interlaminated with grey bioturbated mudstones. 

Calculated values of water in equilibrium with the calcite at the assumed temperature and expressed on the SMOW scale A similar set of measurements of and values for calcites from the Gale Mudstone (tillite) in the Pensacola Mountains was published by Schmidt and Friedman (1974)... 

The succession of versicolor marly mudstones (from V to M) has a high proportion of clay minerals and a low proportion (10-5%) of calcium carbonates (calcite) the sandy structure (C) shows a high proportion of silica (quartz), a variable amount of soft clasts (clays and carbonates) and a low proportion of matrix and cement (<20%) and the sulphated inteiwals (SI and S2) have a variable amount of carbonate ( 20%). All the materials of the outcrop contain a significant quantity of gypsum that acquires a wide diversity of single or twin habits and colours of this mineral. 

The mineralogy of shale, slates, and clays that bloat when subjected to elevated temperatures has been widely reported (Boateng, et al., 1997 Epting 1974). These minerals generally constitute, by volume, 80-97 percent mica clay, 0-10 percent quartz-feldspar, and 2-7 percent accessory minerals, for example, calcite, pyrite, and so on. X-ray analyses have indicated that the major mica-clay constituent of expandable materials is either kaolinite or montmorillonite in still clays, illite and chlorite in the slightly metamorphosed mudstones (shale), and muscovite and chlorite in the more strongly metamorphosed slates. Assays on the raw materials indicate that the oxides may be grouped as shown in Table 10.5. 

For most calcitic samples with wackestone or mudstone texture, Fabricius et al. (2010) observed that measured velocities of water-saturated samples are lower than predicted. They relate the underestimations primarily to the differences in hydraulic radius pore sizes of carbonates with different textures. 

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