Kaolin minerals

The least compHcated clay minerals are the 1 1 clay minerals composed of one tetrahedral (T) layer and one octahedral (O) layer (see Fig. 1). These 1 1 clay minerals are also referred to as TO minerals. The TO package has a basal spacing (nominal thickness) of 0.7 nm (7 E) and they are commonly referred to as 7 E minerals. Kaolinite, the dioctahedral 1 1 mineral, has filling two of three octahedral sites, and serpentine [12168-92-2J, (Mg)3Si205(0H)4, the trioctahedral 1 1 mineral has filling all three octahedral sites. The kaolin minerals have limited substitution in the octahedral... 

Kaolin most commonly originates by the alteration of feldspar or other aluminum siHcates via an intermediate solution phase (97,98) usuaHy by surface weathering (26,99) or by rising warm (hydrothermal) waters. A mica, or hydrated alumina soHd may form as an intermediate phase during the alteration from parent material to kaolin minerals. 

Kaolin minerals (kaolinite, dickite, nacrite), pyrophyllite and mica-rich mica/smec-tite mixed layer mineral occur as envelopes around barite-sulfide ore bodies in the footwall alteration zones of the Minamishiraoi and Inarizawa deposits, northern part of Japan (south Hokkaido) (Marumo, 1989). Marumo (1989) considered from the phase relation in Al203-Si02-H20 system that the hydrothermal alteration minerals in these deposits formed at relatively lower temperature and farther from the heat source than larger sulfide-sulfate deposits in the Hokuroku district. 

The 1 1 kaolin structures are chemically simpler the tetrahedral sites are occupied by silicon and the octahedral sites by aluminum. There is a minor amount of substitution, largely of ferric iron for aluminum, but the amounts are generally only a few tenths of a percent by weight of oxide. The kaolin minerals do not expand in the presence of water and their surface area, approximately 10 to 15 m2/g, represents the external area of the crystals. 

GIESE AND COSTANZO Water on the Surface of Kaolin Minerals... 

Kaolin Minerals. The 1 1 structures include a group of aluminosilicate minerals which are termed collectively the kaolin minerals specifically these are kaolinite, dickite, nacrite, and halloysite. The basic 1 1 layer for all of these minerals has the composition AlgSigOj-fOHJj, there is a small amount of substitution of iron for aluminum, ana fluoride for hydroxyl ion. All, except halloysite, are normally anhydrous and do not expand (as do the smectites) upon exposure to water and most organic molecules. As a result, they generally have a rather small surface area, on the order of 10 nr... 

The types of organic molecules that are able to intercalate the kaolin minerals are generally small with large dipole moments. 

Freeze RA, Cherry JA (1979) Groundwater. Prentice-HaU Englewood Cliffs, NJ Gapon EN (1933) Theory of exchange adsorption in soils. J Gen Chim 3 144-163 Giese RF, Jr. (1982) Theoretical studies of the kaolin minerals Electrostatic calculations. Bull Mineral 105 417 24. 

TOM1TA (K.), TATEYAMA (H.) and OBA (N.), 1970. Formation of vermiculite and kaolin mineral from hornblends. Journ. Jap Assoc. Min. Petr. 

Kaolins. The kaolin minerals include kaolinite. dickite. and nacrite which all have composition AUOi 2 SiO 2 FLO halloysite (7 At. AGO, 2 SiO, 2 H.O and halfoysile (10 A). Al 0, 2 SiO 4 H 0 The struclural formulas for kaolinite and halloysite tIO At. which are shown in Figure I, are AbSiaOiotOH)). and AljSi.iO, i(OH) -4 H,(). respectively. The so-called fire day mineral is a h-axis disordered kaolinite halloysite (7 A) and halloysite (10 A) are disordered along both the a- and h-Mcs Indeed, most variations in the kaolin group originate as structural polymorphs, related to variations in layer slacks. 

Aluminum is the most abundant metallic element in the earth s crust, comprising approximately 8% of the crust (Brusewitz 1984). Aluminum does not occur naturally in the metallic, elemental state, but rather occurs in combination with oxygen, silicon, fluorine, and other elements (Browning 1969 Dinman 1983 IARC 1984 NRC 1982). The most important raw material for the production of aluminum is bauxite, which contains 40-60% alumina (aluminum oxide) (Dinman 1983 IARC 1984). Other raw materials sometimes used in the production of aluminum include cryolite, aluminum fluoride, fluorspar, corundum, and kaolin minerals (Browning 1969 Dinman 1983 IARC 1984). 

DcSousa Santos, P., Brindley, G.W. and De Sousa Santos, H., 1965. Mineralogical studies of kaolinite-halloysite clays, 3. A fibrous kaolin mineral from Piedade, Sao Paulo, BrasiL Am Mineralogist, 50 619—628. 

Hendricks, S.B., 1939a. Crystal structure of nacrite and the polymorphism of the kaolin minerals. Z. Krist., 100 509-518. 

Takahashi, H., 1958. Structural variations of kaolin minerals. Bull. Chem. Soc. Japan, 31 275-283. 

Trivalent cations. By far the most common mineral group of this category is that of the kaolin minerals or Kandite group. The cations involved are solely aluminium which are each linked to three hydroxyl units in one layer and to two oxygens and one hydroxyl in the other. 

Because several spatial stacking arrangements are possible there are several kaolin minerals, each with the same chemical composition, namely Al2Si205(0H)4, but with different properties. Nacrite, dickite, kaolinite, halloysite, and livesite are well recognized species. No positive evidence has so far been published linking other trivalent cations with a single layer lattice structure, but it has been suggested that iron(iii) can replace aluminium in part in the kaolin lattice. 

The main kaolin mineral is kaolinite. The content of coloring ingredients should be low... 

Nespolo M, Takeda H, Kograe T, Ferraris G (1999c) Periodic interrsity distribntion (PID) of mica polytypes Symbohsm, stmctural model orierrtation and axial settings. Acta Crystallogr A55 659-676 Newrrham RE (1961) A refinement of the dickite stmcture and some remarks on polymorphism of the kaolin minerals. Minerd Mag 32 683-704... 

Zvyagin BB (1997) Moditlar analysis of crystal structmes. In Modular aspects of minerals / EMU Notes in Mineralogy, vol. 1. S Merlino (ed) Eotvos University press, Budapesf p 345-372 Zvyagin BB, Drits VA (1996) Interrelated features of stiucture and stacking of kaolin mineral layers Clays Clay Miner 44 297-303... 

Baer AJ (1981) Geotherms - evolution of the lithosphere and plate tectonics. Tectonophysics 72 203-227 Bailey SW (1963) Polymorphism of kaolin minerals. Am Mineralogist 48 1196-1209 Bailey SW, Brown BE (1962) Chlorite polytypism. I. Regular and semirandom one-layer structures. Am Mineralogist 47 819-850... 

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