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Minerals, rocks, discontinuities and rock mass
Published in Ömer Aydan, Rock Mechanics and Rock Engineering, 2019
Chalk is a soft, white, porous form of limestone composed of organic origin. Chalk is formed in shallow waters by the gradual accumulation of the calcite mineral remains of microorganisms such as planktonic green algae, associated with varying proportions of larger microscopic fragments of bivalves, foraminifera and ostracods.
Groundwater environments
Published in Ian Acworth, Investigating Groundwater, 2019
Chalk is a soft, white, porous form of limestone composed of the mineral calcite. It is also a sedimentary rock. It is relatively resistant to erosion and slumping compared to the clays with which it is usually associated, so it forms tall steep cliffs where chalk ridges meet the sea. Chalk hills, known as chalk downland, usually form where bands of chalk reach the surface at an angle, so forming a scarp slope. Chalk is formed in shallow waters by the gradual accumulation of the calcite mineral remains of microorganisms (coccolithophores) over millions of years. Embedded flint nodules are commonly found in chalk beds. The source of the silica in the chert is not clear. The chalk makes up the famous cliffs at Dover in the UK. Figure 1.46 shows the vertically dipping chalk at a location known as The Needles in the west end of the Isle of Wight in the UK. Figure 1.47 shows the chalk overlying older Jurassic deposits on the Isle of Wight.
Soil Chemical Properties
Published in L.B. (Bert) McCarty, Golf Turf Management, 2018
Marl. Marl, also known as bog lime, is mined from shallow, natural deposits of soft calcium carbonates and is often quite moist and impure. Shell marl is bog lime or marl containing numerous shells. When present, marl may become mixed with surface organic soils or peat. These normally acidic organic soils thus become neutral or even alkaline due to the liming action of the marl. Many of the peat or muck sod farms in south Florida, for example, are on soils with marl intermixing. These soils are almost always low in Mg as well as K, P, Cu, and Zn. Marl, when mined for liming purposes, has a neutralizing value between 50% and 90%, depending on the amount of impurities (clay and organic matter) it contains. Oyster shells and other seashells are composed mostly of calcium carbonate and can also make acceptable liming materials when properly pulverized. Chalk is from soft calcitic limestone deposits in oceans.
Pulmonary functions and associated risk factors among school teachers in a selected Nigerian population
Published in International Journal of Occupational Safety and Ergonomics, 2022
Chidiebele Petronilla Ojukwu, Precious Chinecherem Ogualaji, Stephen Sunday Ede, Rita Nkechi Ativie, Chigozie Okwudili Obaseki, Adaora Justina Okemuo, Franklin Onyedinma Irem
Chalk and blackboards are traditional and still the most commonly used teaching aid in most developing countries [13,14]. Chalk (dusty or dustless) is commonly made up of limestone (CaCO3) and/or gypsum (a dehydrated form of CaSO4) as the main constituent. Kaolinite (hydrated aluminum silicate), carboxyl methylcellulose (CMC), polyvinyl alcohol and starch are equally present in lesser quantities. Chalk may also contain some impurities like silica and colored chalks contain some metals, and these chemicals, when inhaled, can expose one to respiratory problems [12]. Teachers using chalk and chalkboards are at risk of developing occupationally related pulmonary function impairments since chalk is a major source of fine particulate matter in the classroom [15], and chalk dust could be harmful to allergic persons and may cause lacrimation and breathing troubles at older age [16].
Production of calcium metal by aluminothermic reduction of Egyptian limestone ore
Published in Canadian Metallurgical Quarterly, 2019
Mohamed H. El-Sadek, K. El-Barawy, I. M. Morsi
The calcium-bearing minerals are occurred in nature either as carbonates (calcite, aragonite and dolomite), as sulphate (gypsum and anhydride) or as fluoride (fluorite or fluorspar). The most abundant mineral is calcite which is the major constituent of the sedimentary rocks (limestone, chalk, marble, dolomite, eggshells and pearls). So, the limestone is used industrially as the main source for calcium metal production [3,4].