Gypsum rocks in Sicily: typology and distribution
Gypsum rocks are widespread all over the world, even if they have different lithological characteristics, origins and ages (from 500 million to a few thousand years).
In Italy, chalky rocks are present in all regions, with outcrops of limited or precise extent and with different ages: from about 250 million years (Upper Permian) to the Messinian Salinity Crisis (about 6 million years ago).
The most significant Italian outcrops are found in Sicily, for an extension of about 1,000 km2 (almost 4% of the regional surface). They are widespread above all in the provinces of Enna, Caltanissetta and Agrigento; chalky outcrops of lesser extent but of great scientific and landscape importance are also present in the provinces of Palermo and Trapani.
In nature, chalky rocks have very different aspects, in relation to the different methods of sedimentation and crystallization. In Sicily it is possible to observe different types:
- Selenitic gypsum: it is made up of transparent crystals with silver reflections, typically twinned in a “dovetail” or “spear shape”.
- Alabaster gypsum: with a compact microcrystalline structure, it has a milky white color and resembles sugar and alabaster.
- Balatino gypsum: consisting of thin sheets of microcrystalline gypsum separated by thin marly and / or carbonate veils.
- Debris gypsum: formed by chalky particles of different sizes, from large crystals to the finest grains of sand.
- Sericulitic gypsum: made up of parallel and elongated fibers, with a silky sheen similar to silk.
The gypsum is found organized in layers of different thicknesses, corresponding to the deposition phases, which can be horizontal or inclined and bent as a result of tectonic events.