gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/002646199548763 Sideronatrite and Metasideronatrite Efflorescence Formed in a Coastal Sea-Spray Environment Garvie L. A. J. Department of Geology, Arizona State University, Tempe, AZ 85287-1404, USA 10 1999 63 5 757 759 17 11 1998 28 1 1999 Copyright © 1999, The Mineralogical Society 1999 Abstract

Sideronatrite [Na2Fe(SO4)2(OH)·3H2O] occurs as yellow botryoidal encrustations on low cliffs of weathered pyrite-bearing mudstones at Barton-on-Sea, Hampshire, England. Extensive areas of the cliffs, up to ∼100 m2, are coated with sideronatrite and its low solubility in cold water secures its longevity. Dry samples of sideronatrite convert readily to metasideronatrite [Na2Fe(SO4)2(OH)·H2O], the reaction to sideronatrite being reversible. Sideronatrite, it is suggested, forms as a result of weathering of pyrite that is present in the argillaceous sediments and reaction with Na from the sea-salt spray.

 Keywords sideronatrite metasideronatrite pyrite weathering efflorescence