Calcite, 3.37

Although calcite crystals exhibit a great variety of Habitus change and many crystal faces are known, the crystal faces maybe grouped as follows. 

The characteristics of the surface microtopography of these faces are schematically illustrated in Fig. 11.6. 

Endo and I. Sunagawa, Positive and negative striations in pyrite, Am. Min., 58,1973, 930-5 

Rostov and R. I. Rostov, Crystal Habits of Minerals, Sofia, Professor Martin Drinov Academic Publishing House and Pensoft, 1999 

Sunagawa, Habit variation in calcite - with special reference to the relation with crystallization sequence. Rep. Geol. Surv., Japan, no. 156,1953 (in Japanese with English abstract) 

Steady-state luminescence of Eu was found in CL spectra (Haberman et al. 1996). Eigure 4.13c represents laser-induced time-resolved luminescence of calcite under 266 nm. Luminescence lines of Eu are seen. Hypersensitive 

---

Terhune R W, Maker P D and Savage C M 1962 Optical harmonic generation in calcite Phys. Rev. Lett. 8 404... 

Calcium. Calcium is the fifth most abundant element in the earth s cmst. There is no foreseeable lack of this resource as it is virtually unlimited. Primary sources of calcium are lime materials and gypsum, generally classified as soil amendments (see Calcium compounds). Among the more important calcium amendments are blast furnace slag, calcitic limestone, gypsum, hydrated lime, and precipitated lime. Fertilizers that carry calcium are calcium cyanamide, calcium nitrate, phosphate rock, and superphosphates. In addition, there are several organic carriers of calcium. Calcium is widely distributed in nature as calcium carbonate, chalk, marble, gypsum, fluorspar, phosphate rock, and other rocks and minerals. 

Hardness. The hardness (qv), or related property abrasiveness, is an important filler property. Hardness is determined by comparison to materials of known hardness on the Mohs scale. On this nonlinear scale, diamond is rated 10, quartz 7, calcite 3, and talc 1. The abrasiveness of a filler is also dependent on psd and the presence of impurities, eg, ka olin clay (Mohs hardness of 3) can be quite abrasive because of the presence of quartz impurities. 

Chemical Bond Formation (Chemisorption). This is the mechanism that leads to the formation of the strongest bonds between coUectors and mineral surfaces. Chemically adsorbed reagents usuaUy form surface compounds at the active waU sites. The flotation of calcite (CaCO ) and... 

The carbonate minerals that comprise limestone ate calcite [13397-26-7] (calcium carbonate), which is easily the most abundant mineral type aragonite [14791-73-2] (calcium carbonate) dolomite [17069-72-6] (double carbonate of calcium and magnesium) andmagnesite [13717-31 -5] (magnesium carbonate). Individual limstone types ate further described by many common names (1). Some of this nomenclature is repetitious and overlapping. The following terms ate in common use in Europe and the United States. 

Calcific limestone is generally used by agronomists to denote a high calcium stone. This term can be misleading, however, because its use could suggest pure calcite, which calcitic limestone usually is not. 

Iceland spar s the purest limestone, virtually pure calcite of about 99.9% CaCO. It is also known as optical calcite its occurrence is rate. 

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. 

Hardness. Most limestone is soft enough to be readily scratched with a knife. Pure calcite is standardized on Mohs scale at 3 aragonite is harder, 3.5—4. Dolomitic limestone is generally harder than high calcium. Dead-burned or sintered limes are 3—4 on this scale, whereas most commercial soft-burned quicklimes are 2—3 (see Hardness). 

Stability. AH calcitic and dolomitic limestones are extremely stable compounds, decomposing only in fairly concentrated strong acids or at calcining temperatures of 898°C for high calcium and about 725°C for dolomitic stones at 101.3 kPa (1 atm). A very mild destabilizing effect is caused by C02-saturated water, as described in the preceding section on solubihty. Aragonite, however, is not as stable as calcite. In sustained contact with moisture,... 

A significant advantage of the PLM is in the differentiation and recognition of various forms of the same chemical substance polymorphic forms, eg, brookite, mtile, and anatase, three forms of titanium dioxide calcite, aragonite and vaterite, all forms of calcium carbonate Eorms I, II, III, and IV of HMX (a high explosive), etc. This is an important appHcation because most elements and compounds possess different crystal forms with very different physical properties. PLM is the only instmment mandated by the U.S. Environmental Protection Agency (EPA) for the detection and identification of the six forms of asbestos (qv) and other fibers in bulk samples. 

Zaire, Norway, and the United States (14). It also occurs with calcite, dolomite, apatite, magnetite, and some siUcates. The density of pyrochlore is ca 4.0—4.4 g/cm. The tantalum content usually is low, ca 0.1—0.3% on a metal basis. 

Carbonate Decomposition. The carbonate content of Green River oil shale is high (see Table 4). In addition, the northern portion of the Piceance Creek basin contains significant quantities of the carbonate minerals nahcoUte and dawsonite. The decomposition of these minerals is endothermic and occurs at ca 600—750°C for dolomite, 600—900°C for calcite, 350—400°C for dawsonite, and 100—120°C for nahcohte. Kinetics of these reactions have been studied (19). Carbon dioxide, a product of decomposition, dilutes the off-gases produced from retorting processes at the above decomposition temperatures. 

Calcite and siderite (27) are used occasionally because of their solubiUty in hydrochloric acid which offers a method of removing mud filter cake deposited on productive formations. Calcite and siderite are used most frequently in workover or completion fluids when a nondamaging fluid is required, ie, one that can be removed by acidising at a later time. 

---