Abstract
Sardinia was affected by an intense igneous activity which generated calc-alkaline products during the Oligo-Miocene period. The volcanic substance shows large variations, ranging from pyroclastic flow deposits, lava flows and domes. By composition, the deposits are all primarily dacites and rhyolites, with subordinate andesites and very scarce basalts. The rhyolite lavas show porphyritic and ash-flow tuffs. Ignimbrite structures are found in the dacitic domes and rhyolitic lavas. These rocks—commercially known as “Trachytes of Sardinia”—used to be quarried in all historical provinces, mainly in the central part of the island to be used as ornamental and building stone. They continue to be commonly used nowadays, but their use dates back to the prehistoric age. They are easily found in many nuraghi, “domus de janas”, holy wells, Roman works (mosaics, paving, roads, bridges), many churches built in Sardinia and practically in all kinds of structural elements in public and private buildings, such as walls, houses, and bridges. Contrary to the granitoid rocks, whose appearance is largely influenced by the mineralogical composition, the aesthetic feature of volcanic rocks is rather affected by the widest range of colors, structure and texture, i.e., shape, size and distribution of mineral components, porphyric index, etc. “Trachyte” is quarried opencast with the “single low step” method, with descending development, with prevalent use of double-disc sawing machines. Whenever the stone deposit allows higher steps, the chain cutting machine, in combination with diamond wire, becomes the preferred extraction solution. This study aims to at look Sardinian “trachytes” from a geoheritage perspective. After a geological-petrographic framework, the paper discusses the historical uses of “trachyte” in Sardinia. The current state of the art of “trachyte” quarrying, processing and usage in the Island is also described. An analysis of the “trachyte” production has been carried out. Finally, a consideration about how to enhance geotourism in the area is suggested.
Highlights
Sardinia was affected by an intense igneous activity which generated calc-alkaline products during the Oligo-Miocene period
Volcanic rocks are very different in commercial field to identify this wide range of stone materials
Volcanic rocks are very different in texture, easy to texture, easy to carve, carve, they have variable porosity, and present very different color features, often characterized by a they have variable porosity, and present very different color features, often characterized by a wide wide variable intensity: Pink, red, yellow, gray, dark gray, green, green-blue
Summary
“Trachyte” is the term which was used to indicate clear, rough rocks outcropping in Greece in the area of Thrace in ancient times [1]. This term is still in use in the Sustainability 2019, 11, 3706; doi:10.3390/su11133706 www.mdpi.com/journal/sustainability. This term is still in use in the commercial field to identify this wide range of stone materials. Stone is a role branch of geoheritage, which with the the preservation that once were the source of such stones.role in human culture and conservationofofhistorical building quarries natural stone resources that had an important supports the preservation of historical quarries that once were the source of such stones
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