Natroalunite occurs typically here as thin lenses of nodules in friable sandstone at or near the Eagle Ford-Woodbine disconformity of the Upper Cretaceous. Typical natroalunite has only traces of impurities; it is exceedingly fine-grained but retains a replica of radial plumose structure which is reflected by the cauliflower-like outer form. Thus, the nodules were derived by transformation from material with spherulitic structures. Minor K 2 O is present, and essential Ca, Sr, Ba, Mg, and rare earths. A deficiency of bases is believed to be compensated for by oxonium H 3 O (super +) ions. The natroalunite is believed to have developed under oxidizing conditions, with pyrite as the source of the SO 4 . Experiments suggest its derivation to be from aluminite.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.