Feldspar Weathering Research Articles

CHARACTERISTICS OF SOME SOLONETZIC SOILS IN THE GLACIAL LAKE EDMONTON BASIN OF ALBERTA

SummaryA mineralogical study was made on five geographically associated Solonetzic and Chernozemic soils from the glacial Lake Edmonton basin.The investigation showed that montmorillonite was generally the dominant mineral present in the clay fraction while illite and kaolinite were next in abundance. Chlorite and interstratified clay minerals were present in very small amounts. The montmorillonite was identified as being transitional between beidellite and nontronite types. The high montmorillonite content of the B horizons of all profiles appeared to have resulted from the preferential translocation of this mineral as well as from chemical transformation of other silicate minerals.The light‐mineral analysis showed weathering of feldspars in the sola although no significant differences were noted in the distribution of heavy minerals.

Studies on the weathering of feldspar in soils derived from gabbro and hornblende-andesite

Studies on the weathering of feldspar in soils derived from gabbro and hornblende-andesite

Reactions of feldspars and micas with aqueous solutions

The weathering of feldspars and micas begins with a series of surface reactions in which metallic cations of the mineral (e.g. Na, K, Ca, Mg) pass into solution in exchange for H ions or other cations. However, many of our simple concepts of exchange reactions fail. For instance, the exchange capacity of feldspar surfaces is not a constant but varies greatly with the exchanging cation. The ammonium ion penetrates the surface readily and gives a high capacity; Mg gives a much lower value. Ammonium also becomes fixed at feldspar surfaces and can then only be removed by boiling in alkali. In all exchange reactions with feldspar surfaces, the previous history was shown to be of great importance. These facts are explained by the formation of a surface layer consisting of somewhat loosened and distorted feldspar chains. The micas, on the other hand, showed much more normal surface exchange. However, the geometry of the exchanging sites was found to be of lay great importance. These were shown to be of more than one kind, characterized by different bonding energies towards cations. Further, the exchangeability of any one cation was highly dependent upon the extent and kind of occupancy of the exchange sites. This was very strikingly shown by curves in which the selectivity numbers were plotted against surface occupancy. These reactions represent the first step in weathering processes, at a stage when new mineral species have not yet made their appearance.

Alkali Soils and Soil Solutions

IN any attempt at agriculture in arid or semi-arid regions, considerable trouble is likely to arise from accumulations of soluble salts at the surface of the soil. The trouble is often intensified by irrigation, and it may become so serious as to counteract the advantages of a reclamation scheme that may be satisfactory in other respects. In a recent issue of the Journal of Agricultural Research, Dr. Breazeale estimates that the losses from this cause have already amounted to one hundred million dollars in the United States alone, and the evil is by no means checked. The soluble salts arise from two causes. Some come direct from the weathering of soda feldspars, diorite, etc.; much, however, arises from the circumstance that the area was once largely covered by marine lagoons or landlocked seas, the water of which evaporated, leaving the salts behind. When the soils are first brought under irrigation, the water applied to the higher levels. is usually excessive in amount, and drains through the lower ground, carrying with it in solution considerable amounts of the chloride, sulphate, carbonate, and bicarbonate of sodium. Calcium carbonate is almost invariably present in the soil, and both sodium chloride and sodium sulphate react with this to produce sodium carbonate, which is much more harmful to vegetation than the other salts. The action is, however, reversible, and the addition of calcium sulphate to the soil has long been a recognised method of reducing the amount of sodium carbonate. The method, however, has not always succeeded, and Dr. Breazeale is able to furnish an explanation from his curves showing the amount of carbonate formed from the various sodium salts. If the carbonate is arising from the interaction of sodium chloride or sodium nitrate with calcium carbonate, then calcium sulphate is effective in bringing about the reversal; if it arises from sodium sulphate, then calcium sulphate is without effect.