Accumulation of carbonates
Crystallization of carbonates takes place through direct precipitation from the soil solutions. Fundamentally three types of crystals can be distinguished:
|Microcrystals. Crystallization produces, in most cases, very small, equidimensional crystals, generally micrite, because normally the precipitation takes place quickly.|
Acicular crystals. In other cases the crystallization produces acicular crystals (from 2 µm in diameter and up to 30 µm long) of calcite, called whiskers.
They occur inside discrete pores (channels, vughs), forming pseudomycelia, build up of a network of more or less interwoven crystals inside the voids.
|They are found preferably in the upper parts of calcitic horizons and represent a very typical case of the crystallization of pedogenic carbonates. They form a first phase of precipitation of carbonates in the soil and are supposed to be formed at the expense of oversaturated solutions.|
|Coarser crystals. Occasionally, when conditions are more favorable for crystallization, carbonates precipitate as crystals of large size (>50 microns).|
Carbonates may be formed as a result of the weathering of Ca-bearing minerals, as it is frequently the case for feldspars.
Plants and animals can synthetize carbonates as secondary products of their metabolism.
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