Halite weathering

For example, lakes in drainage basins of easily weathered soils such as calcareous rocks (calcite, dolomite, gypsum, halite) generally have high values of pH, alkalinity, total dissolved solids, conductivity, and hardness. Such is the case for lakes located in cavities formed through the gradual dissolution of water-soluble rocks (solution or Karst lakes). On the other hand if the drainage basin is in an acidic rock basin (i.e., where silicates predominate and are difficult to weather), the water has an acidic pH, low alkalinity, and low total dissolved solids. 

Natural sources Atmosphere Silicate weathering Pyrite Carbonate Gypsum Halite... 

The simplest weathering reaction is the dissolution of soluble minerals. The water molecule (Box 4.1) is effective in severing ionic bonds (see Section 2.3.2), such as those that hold sodium (Na+) and chlorine (Cl ) ions together in halite (rock salt). We can express the dissolution of halite in a simple way, i.e. ... 

There is limited evidence that halite has been fonnd on rock art although it is more typically encountered as a weathering or alteration crust on art objects. There are also various reports of halite in wall paintings, the origin most probably being from mineral transport or deposition ratiier than specific employment (Kuchitsu and Duan, 1993 Tenmkat, 1994). 

The clear evidence for halite is very interesting in that previous studies of a similar Carboniferous quartz sandstone at nearby Ballycastle by McGreevy (1985) foimd only near-surface accumulations of gypsum in outcrops within the spray zone. In his discussion he noted that of the salts that can be derived from evaporation of sea water, gypsum will crystallize out before salts such as halite and that, if present, halite and other soluble salts will be the first to be removed by rainwater. Other studies of coastal weathering (eg. Mothershead, 1982 and 1989) have inferred the effectiveness of halite in... 

In a 40 m core sample uranium-thorium age dating on layers of ash indicated that the bottom was about 82,000 years (82 kyr) old. At a 6.4 m depth the age was about 8000 years. The amount of mud in the halite from 8-26 kyr indicated that the weather had been comparatively dry, as at present, followed by a brief period of wetter weather. During the period from 64-82 kyr the Salar appeared to have been a saline lake, and the weather was much wetter (Lowenstein et al, 1998). 

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