RASGOS DE ALTERACIóN EN LOS MINERALES DE LAS CENIZAS VOLCáNICAS DEL NORTE DE LA CORDILLERA CENTRAL DE COLOMBIA

this article tries to show some of the characteristics lazy by the physical and chemical weathering of minerals of present volcanic ashes in the sequence the cedral, located to the north part of the "cordillera central of colombia" range. nevertheless, these minerals do not have equal susceptibility to weathering themselves although they are in the same geochemical atmosphere. the weathering degree depends much on its physicochemical structure, of the fragmental size of tephra, the bioclimatic conditions of the site, the topographic position where they have been deposited and of the conditions of drainage, the presence of the preexisting vegetation is equally influential and the microorganisms, all these factors allow that the minerals of volcanic ashes begin their route of weathering. the outstanding characteristics of weathering but in these minerals are: the 1) physical modification of the surfaces, 2) the increase of the specific superficial area, 3) the modification of the edges and forms of crystals, 4) the extensions of cleavage and, 5) the formation of cracks and occlusions. the final consequence of the weathering is the formation of minerals of low degree of crystallization (allophane, imogolite and ferryhidrite, mainly) and the formation of the andisoils, grounds of enormous importance for agriculture.