Amorphous limestone

Amorphous limestone appears to the naked eye to be non-crystalline and to be without form or texture. 

Texture. All limestones are crystalline, but there is tremendous variance in the size, uniformity, and arrangement of their crystal lattices. The crystals of the minerals calcite, magnesite, and dolomite are rhombohedral those of aragonite are orthorhombic. The crystals of chalk and of most quick and hydrated limes are so minute that these products appear amorphous, but high powered microscopy proves them to be cryptocrystalline. Hydrated lime is invariably a white, fluffy powder of micrometer and submicrometer particle size. Commercial quicklime is used in lump, pebble, ground, and pulverized forms. 

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. 

Composite cements may contain mineral additions other than, or as well as, ones with pozzolanic or latent hydraulic properties. Regourd (R34) reviewed the use of ground limestone, which is widely used in France in proportions of up to 27%. The limestones used consist substantially of calcite, with smaller proportions of quartz or amorphous silica and sometimes of dolomite. They must be low in clay minerals and organic matter because of the effects these have on water demand and setting, respectively. The XRD peaks of the calcite are somewhat broadened, indicating either small crystallite size or disorder or both IR spectra confirm the occurrence of disorder. 

Although it constimtes only about 0.09 percent by mass of Earth s crust, carbon is an essential element of living matter. It is found free in the form of diamond and graphite (see Figure 8.17), and it is also a component of natural gas, petroleum, and coal. (Coal is a natural dark-brown to black solid used as a fuel it is formed from fossilized plants and consists of amorphous carbon with various organic and some inorganic compounds.) Carbon combines with oxygen to form carbon dioxide in the atmosphere and occurs as carbonate in limestone and chalk. 

Other inorganic constituents. Many soils, especially in dry climates, are rich in forms of calcium carbonate such as limestone some soils may contain over 50% CaC03. This mineral is quite alkaline and contributes to elevated pH values which may exceed 8.0. Metal oxides in varying amorphous and crystalline forms may also be important constituents of some soils oxisols, for example, may contain as much as 80% Fc203 (Wolfe et al., 1990). Metal oxides may interact with clays and also with organic constituents of soils. 

Silica, amorphous (diatomaceous earth, precipitated and gel silica) Possesses little or no potential to oause silicosis. Most sources of amorphous silica contain quartz (see orystalline silica, below). If greater than 1% quartz is present, the quartz hazard must be addressed. When strongly heated (calcined) with limestone, diatomaceous earth becomes crystalline and can cause silicosis. Amorphous silica has been associated with lung fibrosis, but the role of crystalline silica contamination remains controversial. 10 mg/m (precipitated silica, diatomaceous earth, silica gel) 3 mg/m (respirable dusH 2 mg/m (silica fume) 3000 mg/m White to gray powders. Odorless with a negligible vapor pressure. The TLV for dusts is 10 mg/m if no asbestos and less than 1% quartz ate present. 

Rottenstone ra-t n- Ston (1677) n. Brown, amorphous, siliceous limestone, similar in nature to pumice stone, but softer in texture. Principal uses are as an abrasive and filter medium. 

Arena et al. (1983) and Pis et al. (1991) studied the attrition of amorphous materials such as coal or limestone and found that the size distributions of the attrited materials were independent of the initial particle size and of most operating parameters. Ray et al. (1987a) assumed that unlike crystalline materials, amorphous materials may have some kind of natural grain size to which the degradation finally leads. 

Elemental sulftn- may occur in a number of crystalline and non-crystalline forms, both natural and synthetic in origin. Of these the most important are the amorphous and orthorhombic (Sg) forms. Sulftn is commonly associated with volcanic deposits, particularly during the late stages of vulcanicity around hot springs and pools where it is associated with travertine (. v. a form of limestone), siliceous sinter and borates. It is also found in association with gypsum in sedimentary rocks and particularly with black shales where it is a product of an anaerobic environment and found associated with pyrite (qq.v.). It is also found associated with aerially weathered pyrite (and other similar sulfides) where the rate of oxidation is increased due to the presence of thiobacteria. In these cases it is associated with a range of iron sulfate compounds as well as sulfuric acid. 

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