Nodules in limestones

Chert A hard dense micro- or cryptocrystalline sedimentary rock with interlocking quartz crystals that displays concoidal fracture, prized by hominids as a material for making tools. Occurring as nodules in limestones or dolomites, it is often considered synonymous with flint. Chert is sometimes considered only to be the varieties with visible colors, the cryptocrystalline types, or varieties lacking visible fossil inclusions (see flint). 

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. 

Flint is a common name applied to any material, rock or mineral, that is composed mostly of massive cryptocrystalline quartz. This word is usually used to describe dark-colored chert nodules found in limestones. The term flint is often used by anthropologists to describe homogeneous siliceous materials that have been used to make tools or weapons, regardless of their actual composition. 

Figure 1.A Concentric bands of hematite in a chert nodule in the Madison Group Limestone of Montana. The bands are 1 mm thick. The nodule ( 40 cm across and ovoid in shape) con-...

Country rocks in the Cantung mine area consist of rocks typical of the Selwyn Basin, including turbiditic sandstone, deepwater limestone, chert, shale, and dolostone. Two ore-bearing calcareous units of the Sekwi Formation are bound by argillaceous rocks. In mine terminology, the Swiss Cheese Limestone (SCL) is a calcareous siltstone with chert nodules. The Ore Limestone (OL) conformably overlies the SCL, and is a pure, coarsely crystalline marble up to 50m thick. 

North Africa.—The deposits of Algiers were discovered in 1873 and were fully reported upon in 1886. They are of Eocene age and contain 68 to 68 per cent, of calcium phosphate in a soft rock, together with marl, considerable amounts of silica, calcium fluoride and chloride, nodules of gypsum and almost pure limestone. The beds usually are several feet tflick and run continuously from Morocco to Egypt at a distance of over 100 miles from the sea. Those at Constantine (Algiers) are 120 miles from the port of Bona, and those at Gafsa (Tunis) 150 miles from the port of Stax. 

The Cleveland Member consists primarily of black to brownish-black laminated siliceous shale. It contains minor amounts of calcareous laminae and cone-in-cone limestone. Pyrite is present as nodules, framboids, and irregular forms. Other primary minerals include illite clay and clay- and silt-size quartz. 

The lower unit of the Ohio Shale which is present in the outcrop area of eastern Kentucky is the Huron Member. Primarily, the Huron consists of black to brownish-black to gray-black, laminated, siliceous, OM-rich shales. Calcareous laminae, cone-incone limestone, dolomitic gray shales, dolomite beds and biotur-bated greenish-gray shales occur as interbeds and laminae in the lower parts of the member. Pyrite occurs as framboids, nodules, and irregular forms. 

Typical Pb concentrations in rocks, sods, sediments, and fossil fuels (p-g/g) are basalt, 3 granite, 24 sandstone, 10 limestone, 6 shale, 23 soil, 35 coal 10 sediment, 19. Manganese nodules may contain several hundred p-g/g Pb. In the Earth s crust, the average Pb concentration is estimated to be 15 p-g/g, with 17 pg/g in the upper continental crust, and 13 pg/g in the lower continental crust [26]. Lead is one of the most abundant of the heavy trace elements, for three reasons [27]. First, the cosmic abundance of Pb is relatively high. Second, in addition to common Pb ( Pb), which is non-radiogenic, Pb is derived from the radioactive decay of and Th. In fact, roughly one-half of the ° Pb,... 

Roman cement was the predecessor of today s Portland cement. It was produced by calcining nodules of argillaceous limestone to temperatures below sintering that is, to about 900-1000°C. The binder obtained this way has been called inappropriately Roman cement, even though it in no way resembles the binder in mortars itsed by the... 

In some localities, apatite occurs as nodules on the sea bed, as phosphatic limestone, and in various other forms. These varieties are generally too dispersed or have such a low concentration of apatite that their commercial exploitation does not at present assume much importance. The extent of deep-sea bed apatite has been little explored and available information relates mostly to shallow offshore regions. These regions include Portugal, Morocco, South West Africa, Peru, Chile, southern California, eastern New Zealand, eastern China and eastern United States. Phosphorite is present in snbmerged monntains, mostly in the North Pacific [26-32]. 

Portland cement is a hydraulic cement. Hydraulic cements are defined as cements that not only harden by reacting with water but also form a water-resistant product. Portland cement is produced by pulverising clinkers consisting essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an interground addition. Clinkers are 5-25 mm-diameter nodules of a sintered material which is produced when a raw mixture of limestone and clay is heated to high temperatures (Mehta 1986). The chemical reactions taking place in the cement kiln system can be approximately represented as shown in Fig. 1. 

---