Feldspars deformation

Willaime C. and Gaudais M. (1977). Electron microscope study of plastic defects in experimentally deformed alkali feldspar. Bull Soc. Fr. Mineral Cristallogr., 100 263-271. 

At least a dozen slip systems have been identified by TEM in experimentally and naturally deformed feldspars (see Gandais and Willaime 1984). In many cases, the dislocations are dissociated, though the separation of the partial dislocations is usually small (<50 nm). The dissociation of dislocations of b = [100] gliding in (010) in experimentally deformed sanidine was first observed by Kovacs and Gandais (1980), who suggested the following reactions ... 

Olsen and Kohlstedt (1984) analyzed the dislocations in some naturally deformed intermediate plagioclase feldspars. All the known Burgers vectors except b = [100] were identified, and most, perhaps all, dislocations were dissociated by up to 20 nm. The microstructure was dominated by screw dislocations of b = [001], which had dissociated in (010) probably according to the reaction... 

Gandais, M., Strunk, H. (1983). Microstructure of plastically deformed sanidine (K-feldspar). In Proc. 7th Int. Corf, on High Voltage Electron Microscopy, Berkeley, edited by R. M. Fisher, R. Gronsky, K. H. Westmacott, pp. 353-8. Berkeley (Laboratory), CA, and ENTIS, Springfield, VA. 

Kovacs, M. P., Gandais, M. (1980). Transmission electron microscope study of experimentally deformed K-feldspar single crystals. Phys. Chem. Minerals, 6, 61-76. 

Olsen, T. S., Kohlstedt, D. L. (1984). Analysis of dislocations in some naturally deformed plagioclase feldspars. Phys. Chem. Minerals, 11, 153-60. 

The above evidence establishes that fracturing and seismic behavior can extend well into the zone of mid to lower crustal metamorphism at rock pressures of —0.5-1 GPa. Veins preserve a valuable record of this brittle deformation they are fractures in which mineral mass has been deposited. The most common vein-forming minerals are quartz, calcite, and the feldspars, but a huge variety of other minerals are also observed. Fractures tend to focus flow, because they are zones of elevated permeability. Fracture flow is commonly approximated using the well-known expression from fluid mechanics for laminar flow between two parallel plates (e.g., White, 1979). For a set of parallel fractures, the flux is approximated by (e.g., Norton and Knapp, 1977) ... 

Farley, 2000 Reiners and Farley, 1999, 2001), but this relationship breaks down in samples subjected to intensive ductile or brittle deformation (e.g., Amaud and Eide, 2000 Kramar et al, 2001 Mulch et al, 2002). In general, it seems prudent to assume that a is related to the physical grain size when applying Equations (17) and (19) unless samples show textural evidence for the extensive development of subgrain boundaries that may act as fast diffusion pathways, or— in the case of K-feldspar— show direct evidence of the existence of multiple diffusion domains during incremental heating experiments. 

Reddy S. M., PottsG J., and Kelley S. P. (2001) Ar/ Ar ages in deformed potassioum feldspar evidence of microstruc-tural control on Ar isotope systematics. Contrib. Mineral. Petrol. 141, 186-200. 

The fusion of both potassium and sodium feldspar starts at about the same temperature however, the potassium feldspar melt has a higher viscosity which is maintained up to higher temperatures, so that the ceramic ware is not as readily deformed as when sodium feldspar is used. For this reason, potassium feldspars are preferred in ceramics, while the glass industry requires sodium feldspars which introduce both Na20 and AI2O3 into the glass batch. 

Fast firing, 295 Fayalite, 307, 387 Feldspars, 42—45 Ferric oxide, 32 Ferrite ceramics, 328—333 Ferrites, 328—331,379—380 synthesis of, 331 — 332 Ferroelectric ceramics, 322—327 Ferroelectric glass-ceramics, 236 Ferromagneticceramics, 328—333 Fibre optics, 216 Fibreous insulations, 394 Fibres, 215-217 Fictive temperature, 58 Fireclay, 34, 370-371 Fireclay brick, deformation of, 356—358 Fireclay refractories, 370—373 Firing, 273—297 fast, 295... 

The faulted, non-carbonate cemented sandstones which were sampled from Haltenbanken and Tampen Spur, show clear evidence of diagenetic modifications after the deformation had occurred. Feldspar dissolution, illite precipitation and stylolitization are examples of such diagenetic processes. The pre- and post-faulting diagenetic reactions have been demonstrated to be a useful tool for the purpose of dating fault movements relative to basin subsidence (Sverdrup and Bjprlykke, 1992 Saigal et al., 1995). 

These findings, together with the observation that etch pits are developed in a similar manner on both deformed and undeformed samples of feldspar and calcite (e.g., see Murphy, 1989), indicate that etch pits may only be weakly related to dislocations. Probably, the dense etch pitting observed in natural samples of quartz and silicates must reflect their aqueous chemical environment (i.e., the presence of ligands, which considerably enhance dissolution) and the presence in these solids of localized chemical impurities such as aluminium, which favor the specific adsorption of F and organic ligands as oxalate, silicilate, and similar. This specific adsorption on chemical impurities may result in localized enhancements of dissolution as illustrated by Figure 17. 

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