Glauconitic rocks in the Baltic area: estimation of specific surface

We studied 97 samples from the Baltic area, having varying lithology (limestone, dolomite, dolomitic and calcareous marlstones, and siliciclastics), geological age (Cambrian, Ordovician, Cretaceous, Palaeogene, and Neogene), and thermal history (weakly heated Estonian and Russian samples, more heated Lithuanian samples, and most heated Danish and Polish samples). It was found that the specific surface of glauconite-bearing reservoir rocks could be estimated indirectly from the potassium content as measured by gamma spectrometry, and from magnetic susceptibility. The relationship between the potassium content and specific surface is best defined for a given geological age and thermal history, but is largely independent of lithology. The relationship between magnetic susceptibility and specific surface is best defined for specific lithologies and geological age, but is largely unaffected by thermal history. The thorium and uranium contents as measured by gamma spectrometry gave no clear indication of specific surface.