Potentialities of the biogenic carbonate sands of Porto Santo island for applications in geomedicine
Resumo
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.