Crust efflorescent

The Owens Lake brine analysis of Table V Indicates that the Na/S ratio should be approximately 3.8 for lake bed materials, which agrees quite well with the ambient ratio measured at Keeler. The above data suggests that airborne sulfur aerosols measured in the Owens Valley are in the form of sulfates which are suspended from the efflorescent crust on the Owens Lake bed. Therefore, if we assume that all the sulfur measured at each site is in the form of sulfate, then during a dust storm, the sulfate standard for the state of California (25pg/m ) is violated near the Owens Lake. It should be noted that the sulfate standard was developed for very fine acidic aerosols. The sulfates measured here are larger and basic particles, so their toxicity may be different from particles for which the standard was written. The calculated sulfate levels at each site during a dust storm are listed in Table VI. 

Equations such as equation (1) above imply that the oxidative dissolution of pyrite is congruent, directly liberating Fe2+, SO4, and H+ to solution. However, in the common circumstance that water is insufficiently abundant to immediately transport the oxidation products away from the mineral surfaces, pyrite oxidation more commonly results initially in the accumulation of various hydroxysulphate evaporite minerals. These minerals form efflorescent crusts, typically white and yellow in colour, on the surfaces of pyrite-rich coals and mudstones (Fig. 1), and they effectively store the oxidation products in a readily soluble form until some hydro-logical event delivers sufficient water to dissolve and transport them away. Because pyrite often occurs in mudstones, where Al-bearing clay minerals are in contact with acidic pyrite oxidation waters, A1 is frequently released from the clays and is also stored in these hydroxysulphate phases. When these minerals finally dissolve, they result in abrupt and extreme increases in dissolved acidity. For this reason, they have been termed acid generating salts (AGS) (Bayless... 

Morphological changes observed in the bulk or on the surface of the object are associated with the damages inflicted upon the object debris, dust, superficial deposits, crusts, cracks, pores, fissures, fractures, laminations, lixiviations, spots, efflorescences, etc. (Figs. 1.1 and 1.2). 

Efflorescences or crusts are formed either by the partial or complete drying up of the lakes or ponds during summer, or else by the surface evaporation of subsoil moisture carried to the surface by capillary action. 

This crust formation or efflorescence results in undesirable agglomerate properties [26]. Strength is reduced to that of the bonded hoop at the surface, with the core of the pellet contributing little or nothing (see Section 4.5). Reduced drying rates result from blocked surface pores [3]. Caking tendencies are increased by the high concentration of soluble material in the surface. 

Small crystals of salts are occasionally seen to cover the soil and rocks near springs and seepages. In arid regions such efflorescences, or salt crusts, are also seen on soils in areas detached from springs or other types of surface water. 

Salinity in dryland environment is a natural phenomenon derived from a long-term accumulation of salts on the ground and a lack of adequate flushing in the unsaturated zone. Salt accumulation and efflorescent crusts have been documented in the upper unsaturated zone (e.g., Gee and Hillel, 1988 Nativ et al., 1997 Leaney et al., 2003) and in fracture surfaces (Weisbrod et al., 2000) in many arid areas. The salt formation has been attributed to surface evaporation (Allison and Barnes, 1985), wetting and drying cycles (Drever and Smith, 1978), soil capillarity, and capillarity transport of water and salts from the bulk rock matrix towards fracture surfaces (Weisbrod et al., 2000). 

The various playa environments include a central salt crust or saline pan, composed of dry salt, commonly halite (Figure 10.3D, E), but in some cases trona (Eugster, 1970), gypsum (Stoertz and Ericksen, 1974) or other sulphates such as mirabilite, epsomite or bloedite. The saline mudflat is typically moist clay to silt with surface salt efflorescences and intrasediment (displacive) evaporite minerals. In some systems, these may be zoned on a broad scale, with more-soluble minerals towards the lowest central portion of the mudflat, caused by groundwater evaporation gradients (e.g. Saline Valley, California Hardie, 1968). 

It is perhaps not a surprise to learn that most modem analytical instruments have their place in archaeo-metric and/or conservation research. Many techniques are used extensively to study ceramic and metallic specimens or to identify pitting, weathering crusts, inclusions, efflorescence, and corrosion products on the surface of samples taken from specimens. In addition, the homogeneity of materials of mixed composition is examined, the results of previous restorations are assessed, and the major, minor, and trace element compositions of samples are recorded. A selection of instruments commonly used in archaeology and conservation research is given below. Detailed descriptions of the instruments can be found in the relevant articles in this encyclopedia. 

Watchman et al. (2001) identified epsomite in efflorescent crusts covering rock art at the Carpenter s Gap archaeological... 

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