Potencialidades das areias carbonatadas biogénicas do Porto Santo para aplicações em Geomedicina

Abstract

This paper discloses data concerned with the texture, composition and genesis of the biogenic carbonate sands that occur both in beaches and dunes of the Porto Santo island, Madeira archipelago. These sands that exhibit very small grain size and tabular particle shape, were derived mainly from the fragmentation of coralline algae that did flourish particularly in the NW portion o f the shelf that surrounds the island. The fragmentation referred to was due to the sea waves abrasion that did follow sea level lowering during the Last Great Glaciation. Carbonate sands are mainly composed of magnesian calcite, and strontium rich aragonite occurs as accessory mineral. However, after its formation, aragonite is being inverted gradually into calcite. Specific properties of these sands, either thermal (such as, specific heat, heat diffusivity, and cooling rate), or chemical (such as, chemical composition and dissolution rate), were assessed. The obtained results were considered relevant for applications in geomedicine, under the form of sand-baths in certain conditions. During sand-baths the exuded acid sweat (pH 4.1-6.5) dissolves the carbonate grains liberating Ca, Mg, Sr, P, S and other chemical elements, enabling their absorption through the skin.

No presente trabalho são apresentados dados analíticos relativos à textura, composição, e génese das areias carbonatadas biogénicas que ocorrem em praias e dunas da ilha do Porto Santo, do arquipélago da Madeira. São caracterizadas ainda propriedades específicas destas areias, quer térmicas (tais como, calor específico, difusão do calor e taxa de arrefecimento), quer químicas (por exemplo, composição química e taxa de dissolução química), consideradas relevantes para aplicações em geomedicina, sob a forma de banhos de areia, em determinadas condições.