Gesseira de Santana – Gypsum in Sesimbra

About 200 million years ago the region where today is located the beautiful fishing village of Sesimbra was invaded by sea arms originating large lagoons. The rapid evaporation of the water in this hot and dry environment has led to the accumulation of salts in the bottom of these lagoons; in this case the salt was gypsum.

Gesseira de Santana is the unique occurrence in the municipality of Sesimbra representative of this remote episode.
















This locality corresponds to the former mining of gypsum, which occurs within the marly clays that outcrop in the salvific diapirically of Sesimbra, which was explored by the end of the 50’s to supply the local cement industry.

Gypsum is found in relative abundance in different crystal habits mostly fibrous and saccharoid (granular).










An interesting particularity of this site is the occurrence of small bipiramidal quartz crystals of neoformation at low temperatures, typically associated with clusters of saccharoid crystals habit and whose origin could eventually be related with the existence of a close magmatic vein.



Around these gypsum outcrops I have just found some carbonates apparently calcite and/or aragonite.

A visit is recommended with dry weather. When it rains there are lots of mud and the dense vegetation also doesn’t help.

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