sustainability
Article “Trachytes” from Sardinia: Geoheritage and Current Use
Nicola Careddu 1,* and Silvana Maria Grillo 2
1 Department of Civil, Environmental Engineering and Architecture (DICAAr), University of Cagliari, via Marengo 2, Cagliari 09123, Italy 2 Department of Chemistry and Geology (DSCG), University of Cagliari, via Trentino 51, Cagliari 09127, Italy * Correspondence: [email protected]; Tel.: +39-070-675-5561
Received: 11 June 2019; Accepted: 4 July 2019; Published: 6 July 2019
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.
Keywords: pyroclastic rock; dimension stone; Sardinia; geoheritage; market
1. Introduction “Trachyte” is the term which was used to indicate clear, rough rocks outcropping in Greece in the area of Thrace in ancient times [1]. Another etymological interpretation of the word might derive from the Greek word “τυραχζ” which means “rough”. From the petrographic point of view, trachyte is the volcanic equivalent of syenites, which are rocks formed with K-feldspar, subordinate plagioclase oligo-andesinic and mafic, such as green hornblende and biotite. Quartz is generally missing. Differently, “Trachite auctorum” is the latin term which, in the past, indicated a multiplicity of vulcanites, from acidic to neutral (rhyolites, riodaciti, dacites and andesites), found in Central and North-Central Sardinia (Ottana, Sedilo, Allai, Fordongianus, Bosa, Ozieri, Oschiri and Osilo), southern (Serrenti) and southwestern (Sulcis) as shown in Figure1. This term is still in use in the
Sustainability 2019, 11, 3706; doi:10.3390/su11133706 www.mdpi.com/journal/sustainability Sustainability 2019, 11, x FOR PEER REVIEW 2 of 17
SustainabilityNorth-Central2019, 11Sardinia, 3706 (Ottana, Sedilo, Allai, Fordongianus, Bosa, Ozieri, Oschiri and Osilo),2 of 16 southern (Serrenti) and southwestern (Sulcis) as shown in Figure 1. This term is still in use in the commercial field to identify this wide range of stone materials. Volcanic rocks are very different in commercial field to identify this wide range of stone materials. Volcanic rocks are very different in texture (lavas, ignimbrites, pyroclastic rock welded in different ways, stagnation dome), easy to texture (lavas, ignimbrites, pyroclastic rock welded in different ways, stagnation dome), 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. variable intensity: Pink, red, yellow, gray, dark gray, green, green-blue.
Figure 1. Lithological map of Oligo-miocenic volcanite outcrops and localities mentioned in the text (elaboratedFigure 1. Lithological by Authors from map [2 ]).of Oligo-miocenic volcanite outcrops and localities mentioned in the text (elaborated by Authors from [2]). The aim of this study is to highlight how the “trachytes” of Sardinia can be regarded as a heritage stoneThe resource aim of (HSR). this study HSR is to a naturalhighlight stone, how which the “trach was usedytes” inof theSardinia construction can be regarded of historical as a buildings heritage andstone monuments resource (HSR). over an HSR extended is a periodnatural of stone, time (sometimeswhich was centuries) used in andthe thatconstruction should be of involved historical in abuildings great deal and of monuments consideration over for an its extended use in the period restoration of time of (sometimes those same centuries) historical and buildings—when that should be necessary—eveninvolved in a great when deal local of quarriesconsideration may no for longer its use be in active the [restoration3,4]. It is exactly of those for thissame reason historical that anbuildings—when international category necessary—even has been when created local to includequarries those may globalno longer natural be active heritage [3,4]. stone It is exactly resources for (GHSR)this reason that that have an achieved international widespread category utilization has been in created human to culture include [5]. those global natural heritage stoneThe resources present (GHSR) study is that considered have achieved a geoheritage widespread subtopic; utilization geoheritage in human can culture indeed be[5]. defined as a the branchThe present of geosciences study is that considered studies “Globally,a geoheritage nationally, subtopic; state-wide, geoheritage the regionalcan indeed features be defined of geology as a suchthe branch as its igneous, of geosciences metamorphic, that studies sedimentary, “Globally, stratigraphic, nationally, structural, state-wide, geochemical, the regional mineralogic, features of paleontologic,geology such geomorphic,as its igneous, pedologic, metamorphic, and hydrologic sedimentary, attributes stratigraphic, at all scales, structural, that are geochemical, intrinsically importantmineralogic, or culturallypaleontologic, important, geomorphic, which o ffpedologic,er information and orhydrologic insights into attributes the formation at all scales, and evolution that are ofintrinsically the Earth, orimportant into the or history culturally of science, important, or which whic canh offer be used information for research, or insights teaching into or reference”the formation [6]. Forand theseevolution reasons, of the heritage Earth, or stone intois the a branchhistory ofof geoheritage,science, or which which can deals be used with for the research, conservation teaching of buildingor reference” natural [6]. stone For these resources reasons, that heritage had an importantstone is a rolebranch in humanof geoheritage, culture andwhich also deals supports with thethe preservationconservation ofof historical building quarriesnatural stone that once resources werethe that source had an of suchimportant stones. role in human culture and also supports the preservation of historical quarries that once were the source of such stones. Historical and Current Uses 1.1 HistoricalThese rocks and have Current been Uses widely used since ancient times, and can be found in numerous constructions locatedThese throughout rocks have the island. been Awidely great use used of it wassince done ancient during times, the Roman and can age: be For found example, in thenumerous ancient thermalconstructions baths located of Fordongianus, throughout shown the island. in Figure A grea2, whicht use of were it was built done with during squared the grey Roman boulders age: For of “trachyte” [7], as well as the seven-arches bridge over the river Tirso, which was built with “trachyte” on top of an older bridge; Sardinian “trachyte” was also used by the Romans for the composition of Sustainability 2019, 11, x FOR PEER REVIEW 3 of 17 example, the ancient thermal baths of Fordongianus, shown in Figure 2, which were built with squared grey boulders of “trachyte” [7], as well as the seven-arches bridge over the river Tirso, which Sustainabilitysquared grey2019 boulders, 11, 3706 of “trachyte” [7], as well as the seven-arches bridge over the river Tirso, which3 of 16 was built with “trachyte” on top of an older bridge; Sardinian “trachyte” was also used by the Romans for the composition of mosaics and flooring in Nora. There is extensive footage of ancient “trachyte”,mosaics and used flooring in prehistory in Nora. There to build is extensive defensive footage walls ofbuilding, ancient “trachyte”,“Domus de used Janas” in prehistory(i.e., fairies’ to house),build defensive stone huts, walls nuraghi building, (i.e., “Domus Santu Antine, de Janas” shown (i.e., in fairies’ Figure house), 3, which stone is one huts, of the nuraghi biggest (i.e., and Santu best Antine,preserved shown nuragic in Figure settlements3, which of the is one island), of the carved biggest vases and best(currently preserved exhibited nuragic at the settlements local Sardinian of the museums),island), carved mostly vases dating (currently back exhibited to what atis thegenerall localy Sardinian referred museums),to as the “cultura mostly datingdi Ozieri” back (middle to what Neolithic),is generally etc. referred to as the “cultura di Ozieri” (middle Neolithic), etc.
FigureFigure 2. Forum 2. Forum Traiani, Traiani, Ancient Ancient Roman Roman thermal thermal bathsbaths in in Fordongianus Fordongianus (I–III (I–III centuries centuries a.c). a.c).
Figure 3. 3.Santu Santu Antine Antine nuraghe, nuraghe, near near Torralba Torralba (North-West (North Sardinia).-West Sardinia). It was built It was from built 1800 from to 1450 1800 b.c. to 1450 b.c. Important examples of the use of these volcanic rocks, which are used in construction as well as by architects,Important can examples be typically of the seen use in of the these civic volcanic center ofro severalcks, which Sardinian are used towns: in construction “Trachytes” as are well used as byto makearchitects, different can be architectural typically seen parts in inthe both civic public center and of several private Sardinian buildings, towns: as ashlars, “Trachytes” pillars, are capitals, used toarchitraves, make different jambs, architectural statues, friezes parts and in etc.both A public special and mention private should buildings, be made as ashlars, of the pillars, manychurches capitals, architraves,built in the 12thjambs, and statues, 13th centuries, friezes and that etc. can A be special considered mention a showcase should be where made the of the visitor many can churches observe builtthe “trachytes” in the 12th inand all 13 shapesth centuries, and sizes; that somecan be examples considered are showna showcase in Figure where4a–c. the visitor can observe the “trachytes” in all shapes and sizes; some examples are shown in Figure 4a–c.
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(a) (b) (c)
Figure 4.4. AncientAncient(a) Roman Roman bridge bridge in in Sant’Antioco Sant’Antioco(b) ((aa).). It It was was restored restored in in 1858, (c) 1858, 1893 1893 and and 1920; 1920; The ChurchChurch of(a) of San San Pietro Pietro extra extra muros muros in Bosa in(b) (north-westBosa (north-west Sardinia, Sardinia, XI-XIII centuries) XI-XIII(c) centuries) (b). It was built(b). Figure 4. Ancient Roman bridge in Sant’Antioco (a). It was restored in 1858, 1893 and 1920; in Romanesque style by using various shades of pink and red rhyolites; (c) Fort Sabaudo, Sant’Antioco It wasTheFigure built Church 4 in. Ancient Romanesque of San Roman Pietro bridgestyleextra bymuros in usingSant’Antioco in Bosavarious (north-west (a ).shades It was restoredofSardinia, pink andin XI-XIII 1858, red 1893 centuries)rhyolites; and 1920; ( bc)). Fort (built in 1813–1815). Sabaudo,ItThe was Church Sant’Antioco built in of Romanesque San Pietro (built extra in style 1813 muros by– using1815). in Bosa various (north-west shades of Sardinia, pink and XI-XIII red rhyolites; centuries) c) Fort (b). Sabaudo,It was built Sant’Antioco in Romanesque (built style in 1813–1815). by using various shades of pink and red rhyolites; c) Fort The main areas where “trachytes” are currently quarried and processed are practically near to The mainSabaudo, areas Sant’Antioco where “trachytes” (built in 1813–1815). are currently quarried and processed are practically near to historic sites, sites,The whichmain which areas follow follow where the the “trachytes” geological geological aredistribution distribution currently quarried of ofoutcrops. outcrops. and processed The The main main are production practically production facilities near facilities to for bothfor both historicornamental ornamentalThe sites, main whichuse areas use and follow where and construction constructionthe“trachytes” geological are are distribution are currentlylocate locatedd in quarriedof in Fordongianusoutcrops. Fordongianus and The processed main (near (near production are Oristano) Oristano) practically facilities and and near Serrenti for to (Campidano)bothhistoric ornamental sites, where which theuse follow quarryingand constructionthe geological activity are distribution has locate startedd in of againagain Fordongianus outcrops. aboutabout The twentytwenty (nearmain production yearsyearsOristano) ago.ago. and facilities Serrenti for both ornamental use and construction are located in Fordongianus (near Oristano) and Serrenti With(Campidano) regard whereto the the latter, quarrying which activity is currently has started beingbein gagain reassessed, about twenty it is quarriedyears ago. to obtain the stone (Campidano)With regard where to thethe latter,quarrying which activity is currently has started being again reassessed, about twenty it is quarried years ago. to obtain the stone known as “Pietra di Serrenti”, a a light-grey pyroclastic pyroclastic andesite, andesite, which which is is easy easy to to be be carved carved and and split; split; knownWith as “Pietraregard todi theSerrenti”, latter, awhich light-grey is currently pyroclastic bein gandesite, reassessed, which it is is quarried easy to be to carvedobtain andthe stonesplit; it has been quarried and processed by skilled stonemasons since the 19thth century from the quarry of it has been quarried and processed by skilled stonemasons since the 19th century from the quarry of Monteitknown has Atzorcu been as “Pietra quarried and used di Serrenti”and to processed build, a thelight-grey by traditional skilled pyroclastic stonemasons portals andesite, of bothsince which Serrentithe 19 is easycentury houses to be from including carved the quarryand the split; housesof MonteMonteit Atzorcuhas been Atzorcu quarriedand and used used and to buildprocessedto build the the traditionalby traditional skilled stonemasons portportals ofof both bothsince Serrenti Serrentithe 19th houses century houses including from including the the qua housestherry housesof (Figure5), the old market hall and the local Court of Justice in Cagliari (shown in Figure6), a part (Figure(FigureMonte 5), the Atzorcu 5), oldthe oldmarket and market used hall to hall buildand and th the the e localtraditional local Court Court port ofof alsJustice of both in in Cagliari CagliariSerrenti (shown houses (shown inincluding Figurein Figure 6), the a 6),housespart a partof of theof the porticothe(Figure portico portico of 5), ofVia the of Via ViaoldRoma, Roma, marketRoma, the the thehall churches churcheschurches and the oflocal of of San San San Court FranceFrance Francesco of Justicesco (in(in (in in Cagliari, Cagliari, Cagliari Cagliari, too), (shown too), too), squares, squares, squares,in Figure and and and6),an aarray an anpart array array of of monumentsmonumentsthe portico all over ofall Viaover Campidano, Roma, Campidano, the churches etc. etc. of San Francesco (in Cagliari, too), squares, and an array of
(a) (b)
(a) (b) Figure 5. (a)(a and) (b): two examples of houses, (a) and ((b),b) built by using “Pietra di FigureFigure 5. (a) 5. and (a)( andb): two (b): examplestwo examples of houses, ofSerrenti”. houses, (a) and (a) (andb), built (b), built by using by using “Pietra “Pietra di Serrenti”. di Figure 5. (a) and (b): two examples ofSerrenti”. houses, (a) and (b), built by using “Pietra di Serrenti”.
Figure 6. Court of Justice in Cagliari, built in 1938 by using also the “Pietra di Serrenti”.
Figure 6. Court of Justice in Cagliari, built in 1938 by using also the “Pietra di Serrenti”. Sustainability 2019, 11, 3706 5 of 16
It should be noted that all the different Sardinian “trachytes” started to be utilized at different momentsSustainability throughout 2019, 11, x FOR history. PEER REVIEW For example, Fordongianus “trachytes” have been used since5 of 17 Roman times and the Pietra di Serrenti since 19th century, while the use of Red Montresta in building is relativelyFigure recent. 6. Court of Justice in Cagliari, built in 1938 by using also the “Pietra di Serrenti”.
2. GeologicalIt should Framework be noted that all the different Sardinian “trachytes” started to be utilized at different moments throughout history. For example, Fordongianus “trachytes” have been used since Roman timesFigure and1 theshows Pietra the di lithological Serrenti since map 19th of century, volcanics while in Sardinia,the use of whichRed Montresta are related in building to two diis fferent volcanicrelatively cycles: recent. A Plio-Pleistocenic one and a Oligo-Miocenic the second. The first cycle occurred abundantly in the mid-western part of Sardinia and started when the island began2. Geological to separate Framework from the European continental mass during the Lower Oligocene. The subsequent openingFigure of the 1 Balearicshows the basin lithological activated map a subductionof volcanics zonein Sardinia, to which which the are main related phase to two of this different volcanism is linked.volcanic This cycles: volcanic A Plio-Pleistocenic phase is composed one and of a twoOligo-Miocenic main complexes the second. both starting with mainly andesitic brecciasThe and first lavas, cycle followedoccurred abundantly by more felsic in the product mid-western as tu partff, lavas of Sardinia and ignimbrites. and started when Most the of these productsisland arebegan subaerial. to separate However, from the during European the restcontinental of Miocene, mass aduring marine the transgression Lower Oligocene. with depositionThe of sedimentssubsequent asopening conglomerate, of the Balearic sandstone, basin activated clay and a subduction limestone zone covered to which most the of main these phase outcrop of this [8 –11]. volcanism is linked. This volcanic phase is composed of two main complexes both starting with These volcanic activity can be shared in different phases: mainly andesitic breccias and lavas, followed by more felsic product as tuff, lavas and ignimbrites. MostA first of these sequence products from are 32 subaerial. My: Outcrops However, in du Central-Westring the rest andof Miocene, South Sardinia,a marine transgression is characterized by • withlava deposition with an of intermediate sediments as toconglomerate, basic chemistry. sandstone, These clay rocks and limestone generally covered present most a dome of these structure, outcrop [8–11]. which is often associated with pyroclastic sediments. These volcanic activity can be shared in different phases: The• second acid explosive from 23 My: Characterized by volcanic products essentially dacitic • A first sequence from 32 My: Outcrops in Central-West and South Sardinia, is characterized to rhyolitic,by lava ignimbriteswith an intermediate and subordinate to basic chem lavas.istry. This These sequence rocks generally outcrops present in several a dome parts of Centralstructure, Sardinia. which is often associated with pyroclastic sediments. The• thirdThe sequencesecond acid goes explosive from 19 from to 16 23 Ma: My: Prevalent Characterized outcrops by volcanic in Western, products Central essentially and Southern • Sardinia.dacitic Here, to volcanicrhyolitic, rocksignimbrites are composed and subordinate by andesites lavas. andThis basaltssequence that outcrops have been in several deposited by meansparts of lava of Central flows andSardinia. pyroclastic sediments, both subaqueous and subaerial, or as lava domes • The third sequence goes from 19 to 16 Ma: Prevalent outcrops in Western, Central and and associated explosive phreatic-magmatic products. Southern Sardinia. Here, volcanic rocks are composed by andesites and basalts that have The last activity between 17 and 13 Ma is characterized by ignimbritic, pyroclastic and lava-like • been deposited by means of lava flows and pyroclastic sediments, both subaqueous and rocks.subaerial, These products or as lava are domes riolitic and and associ daciticated (with explosive rare episodesphreatic-magmatic of pyroclastic products. sedimentation with sanidine),• The last sometimes activity between commenditic 17 and (Sulcis).13 Ma is characterized by ignimbritic, pyroclastic and lava- like rocks. These products are riolitic and dacitic (with rare episodes of pyroclastic All thesesedimentation volcanic productswith sanidine), have sometimes subalkaline commenditic affinity as(Sulcis). shown in the Middlemost diagram of FigureAll7 .these This volcanic diagram products has been have successfully, subalkaline af andfinity often as shown compared in the Middlemost to the original diagram definition of of MiddlemostFigure 7. This [12], whichdiagram reported has been only successfully, alkaline series and [often13]. compared to the original definition of
Figure 7. Middlemost (1975) summary diagram of all oligo-Miocene volcanics of Sardinia (elaborated by Columbu et al. [13]). Sustainability 2019, 11, x FOR PEER REVIEW 6 of 17 Sustainability 2019, 11, 3706 6 of 16 Figure 7. Middlemost (1975) summary diagram of all oligo-Miocene volcanics of Sardinia (elaborated by Columbu et al. [13]). In summary, dacitic to rhyolitic ignimbrites are the prevailing products of volcanic activity, followedIn bysummary, andesitic, dacit basalticic to rh andesiticyolitic ignimbrites and, finally, are basaltic the prevailing lavas [11 ].products of volcanic activity, followedFigure 8bya–f andesitic, shows thebasalt micro-photographiesic andesitic and, finally, under basaltic crossed lavas [11]. polars of six di fferent Sardinian “trachytes”;Figure their 8a–f di showsfferences, the explainedmicro-phot inographies the figures under caption, crossed are clear.polars of six different Sardinian
(a) (b)
(c) (d)
(e) (f)
FigureFigure 8. 8Thin. Thin section section micro-photographies micro-photographies for somefor some representative representative samples samples of Early of MioceneEarly volcanicMiocene rocks volcanic from Sardinia. rocks from The observedSardinia. mineralThe observed phases aremineral euhedral phases to subhedral are euhedral K feldspar, to plagioclase,subhedral quartz, K feldspar, horneblende plagioclase, in a groundmass quartz, horneblende from hypohyaline in a groundmass (Ploaghe from (a), Sant’Antioco hypohyaline (b )) to(Ploaghe hypocrystalline (a), Sant’Antioco (Fordongianus (b)) red to (hypocrystallinec), Carloforte (d ),(Fordongianus Allai (e)) showing red (c) a porphyritic, Carlofortetexture (d), andAllai diff erent(e)) showing porphyric a porphyritic index. In the texture Serrenti and area, differen the andesitict porphyric rocks, index. which In the include Serrenti domes area, and volcaniclasticthe andesitic products, rocks, iswhich interested include by epithermaldomes and phenomena, volcaniclastic so theproducts, outcrops is areinterested interested by by propiliticepithermal alteration phenomena, and silicification so the (foutcrops). Legend: are pl =interestedplagioclase; by Kfspropilitic= alkali alteration feldspar:sanidine; and qz = quartz, hb = hornblende. Sustainability 2019, 11, x FOR PEER REVIEW 7 of 17 Sustainability 2019, 11, 3706 7 of 16 silicification (f). Legend: pl = plagioclase; Kfs = alkali feldspar:sanidine; qz = quartz, hb =
hornblende.Sustainability 2019 , 11, x FOR PEER REVIEW 7 of 17 3. State of Art 3. StatePyroclastic ofsilicification Art rock (f) are. Legend: widely pl quarried = plagioclase; in all Kfs the = historical alkali feldspar:sanidine; provinces of theqz = Island,quartz, mainlyhb = in the hornblende. areasPyroclastic of Fordongianus-Allai, rock are widely Ottana, quarried Sedilo, in all Ozieri the historical and Serrenti provinces as ornamental of the Island, stone mainly and building in the stoneareas3. bothof State Fordongianus-Allai, as of aggregates Art and ashlars.Ottana, Sedilo, Ozieri and Serrenti as ornamental stone and building stoneThe both beauty as aggregates of Sardinian and “Trachyte” ashlars. lies in its warms colors, whose intensity may vary even within Pyroclastic rock are widely quarried in all the historical provinces of the Island, mainly in the a singleThe quarry beauty run, of aSardinian single slab “Trachyte” and therefore lies ain single its warms product, colors, enhancing whose the intensity unique charactermay vary of even this areas of Fordongianus-Allai, Ottana, Sedilo, Ozieri and Serrenti as ornamental stone and building natural stone. withinstone a single both as quarry aggregates run, and a ashlars.single slab and therefore a single product, enhancing the unique characterColor Theof variability this beauty natural of of Sardinian Sardinianstone. “Trachyte” “trachytes” lies is in neither its warms a defect, colors, nor whose a limit, intensity but a very may peculiar vary even feature of thisColorwithin type variability ofa single material quarry of that Sardinian isrun, skillfully a single “trachytes” used slab forand building istherefore neither and aa single ornamentaldefect, product, nor purposes.a limit,enhancing but It shouldathe very unique bepeculiar noted thatfeature thecharacter of variability this oftype this ofof natural colormaterial isstone. extremely that is skillfully common; used there for are building so many and intermediate ornamental and purposes. softened It should shades amongstbe noted aColorthat vast thevariability range variability of colorsof Sardinian of [14 color]. “trachytes” is extremely is neither common; a defect, there nor are a limit, so many but a intermediatevery peculiar and softenedAccordingfeature shades of this toamongst type the of various material a vast genetic rangethat is ofskillfully processes, colors used[14]. appearance for building andand ornamental texture may purposes. vary, not It should only from typeAccordingbe to type,noted butthat to even thethe variability various within thegenetic of samecolor processes, is commercial extremely appearance common; type. This thereand is madetextureare so possiblemany may intermediatevary, by thenot orientationonly and from softened shades amongst a vast range of colors [14]. intype which to type, the quarrymanbut even within makes the the same cuts, commercial which can betype. enhanced, This is made emphasized possible or by minimized the orientation the role in According to the various genetic processes, appearance and texture may vary, not only from ofwhich constituents the quarryman of each makes material the (crystals,cuts, which lithic can fragments, be enhanced, veins emphasized etc.). A good or minimized example is the provided role of type to type, but even within the same commercial type. This is made possible by the orientation in by the “trachyte” Red Montresta, which looks very different depending on the direction of the cut constituentswhich the of quarryman each material makes (cry thestals, cuts, lithicwhich fragments, can be enhanced, veins emphasized etc.). A good or minimizedexample is the provided role of by (Figurethe “trachyte”constituents9a,b). Red of each Montresta, material (crywhichstals, looks lithic fragments,very different veins dependingetc.). A good on example the direction is provided of bythe cut (Figurethe 9a,b).“trachyte” Red Montresta, which looks very different depending on the direction of the cut (Figure 9a,b).
(a()a ) (b()b )
FigureFigure 9.9. AppearancesAppearances 9. Appearances of of “trachyte” of“trachyte” “trachyte” Red RedRed Montresta: Montresta:Montresta: (a) (a) Sample(a) Sample Sample cut cut parallel cut parallel parallel to to the theto flow flowthe planes, flow (planes,b) sampleplanes, (b) cut sample(b) orthogonal sample cut cut orthogonal to orthogonal the flow planes. to to the the Both flowflow the planes.planes. samples Both Both have the the asamples saw-planesamples have have surface. a saw-plane a saw-plane surface. surface. The use of “trachyte” has its roots in ancient times, when it was used to make external paving, The use of “trachyte” has its roots in ancient times, when it was used to make external paving, which has coupled to the use of cladding in contemporary times (as shown in Figure 10). Thewhich use has of coupled “trachyte” to the has use its of claddingroots in ancientin contemporary times, when times it(as was shown used in toFigure make 10). external paving, which has coupled to the use of cladding in contemporary times (as shown in Figure 10).
Figure 10. A detail of Teatro Massimo in Cagliari; the cladding, installed following a “run” pattern with runs in variable heights, was built using Fordongianus red “trachyte” (renewed in 2009).
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SustainabilityFigure2019 10.,. 11AA, detail 3706detail ofof TeatroTeatro MassimoMassimo inin Cagliari;Cagliari; thethe cladding,cladding, installedinstalled followingfollowing aa “run”“run”8 of 16 pattern with runs in variable heights, was built using Fordongianus red “trachyte” (renewed(renewed inin 2009).2009). Using this pyroclastic rocks to build stairs best enhances the properties of various types; in fact, it is representativeUsing this pyroclastic of all the various rocks to surface build finishesstairs best that enhances can be made, the properties ranging from of various the mild types; thicknesses in fact, itofit is theis representativerepresentative covered steps toofof theallall onethethe ofvariousvarious the solid surfacesurface steps infinishesfinishes any shape thatthat (rectangular, cacann be made, triangular, ranging fan-shaped, from the mild etc.) thicknessesandthicknesses any edge ofof profiling. thethe coveredcovered stepssteps toto thethe oneone ofof thethe solidsolid stepssteps inin anyany shapeshape (rectangula(rectangular,r, triatriangular,ngular, fan-shaped,fan-shaped,Another etc.)etc.) important andand anyany use edgeedge is beautifully profiling.profiling. summed up both by celebratory and commemorative works of art,Another such as important monuments use and is sculptures beautifully (Figure summed 11a,b), up and both by by other celebratory works that and are commemorative able to combine worksfunctionality, of art, such designsuch asas and monumentsmonuments sensitivity andand for sculptures naturalsculptures stone, (Figure (Figure as is 11a,b), the11a,b), case and a withnd by by someother other fountains.works works that that are a reable able to tocombine functionality, design and sensitivity for natural stone, as is the case with some fountains.
((a)) ((b))
Figure 11. 11.( a(a)) Parco ParcoParco delle delledelle Rimembranze RimembranzeRimembranze (Cagliari), (Cagliari),(Cagliari), the monument thethe monumentmonument was built waswas with builtbuilt Bosa withwith red “trachyte”; BosaBosa redred (“trachyte”;b) two sculptures (b)(b) twotwo in Pietrasculpturessculptures di Serrenti inin PietraPietra at San didi Sperate SeSerrentirrenti (Cagliari). atat SanSan SperateSperate (Cagliari).(Cagliari).
Sardinian “trachytes” areare also used in a wide wide rang rangee of of architectural architectural components components as as arches, arches, jambs, jambs, columns,columns, pillarspillars (Figure(Figure 1212).12).).
Figure 12. 12..Some SomeSome examples examplesexamples from fromfrom a private aa privateprivate building buildingbuilding showing showingshowing a combination aa combinationcombination of Red Montresta ofof RedRed MontrestaMontresta “trachyte” with“trachyte” Orosei marblewith Orosei (courtesy marble of Marmi (courtesy & Pietre of I.C.S.Marmi s.r.l. & [Pietre15]). I.C.S. s.r.l. [15])
InIn recentrecent years,years, productionproduction has has proved proved to to bebe particularlyparticularly prolificprolificprolific inin thethe segmentsegment ofof furnishingfurnishing accessories, forfor which which has has supported supported the developmentthe developme of ant whole of a rangewhole of range interesting of interesting lines of production. lines of production.It includes both It includes objects both with objects a strong with aesthetic a strong vocation, aesthetic such vocation, as rose such windows, as rose cornices, windows, inlay cornices, works, fretworks, etc., which combine aesthetics with functionality, such as clocks (wall, table), mirrors, tables of all sizes, fireplaces, bathroom sets, tops and elements for kitchens.
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Among the furnishing accessories, a new concept of mosaic was developed in bathroom fittings, kitchen countertops, tables, fountains and with stone elements. Sardinian “trachytes” are often associated with other stones, including basalt and travertine, a material particularly appreciated by the antiqued finishing.
3.1. Quarrying As stated above, the commercial name “Sardinian Trachyte” covers a wide variety of pyroclastic rocks that henceforth will all be referred to by their common trade name. Currently, the Sardinian market offers a number of “trachyte” stone types, which come in different grains, hardness, compactness and colors (pink, red, yellow, gray, brown; less frequently, green-blue); Figure 13 shows some Sardinian “trachytes” which are important from an historical and commercial point of view. Moreover, as we look at Figure 13, it is interesting to see how geodiversity, regarded as the naturalSustainability range 2019 (diversity), 11, x FOR ofPEER geological REVIEW rocks [16] and relative properties, is embedded in geoheritage. 10 of 17
FigureFigure 13. Some13. Some hystorical hystorical and commercialand commercial Sardinian Sardinian “trachytes”: “trachytes”:1) Carloforte, 1) Carloforte,2) Red Montresta,2) Red 3) FordongianusMontresta, 3) Fordongianus red, 4) Allai, red,5) Fordongianus 4) Allai, 5) Fordongianus green, 6) Ozieri, green, 76)) Ozieri, Bosa, 8 7)) PietraBosa, 8) di Pietra Serrenti, 9) Fordongianusdi Serrenti, 9) gray, Fordongianus10) Carbonia-Perdaxius, gray, 10) Carbonia-Perdaxius,11) Sant’Antioco, 11)12) Ploaghe.Sant’Antioco, 12) Ploaghe.
“Trachyte” is quarried and worked by companies located in the provinces of Oristano (Ardauli, Bosa, Fordongianus, Ruinas), Sassari (Benetutti, Ittiri, Oschiri, Ozieri, Uri), Cagliari (Serrenti, whose local quarry is shown in Figure 14), and Nuoro (Sedilo). Sardinian deposits are usually extensive and only slightly fractured, with exploitable depths ranging from 10 up to 65 m [17].
Sustainability 2019, 11, 3706 10 of 16
“Trachyte” is quarried and worked by companies located in the provinces of Oristano (Ardauli, Bosa, Fordongianus, Ruinas), Sassari (Benetutti, Ittiri, Oschiri, Ozieri, Uri), Cagliari (Serrenti, whose local quarry is shown in Figure 14), and Nuoro (Sedilo). Sardinian deposits are usually extensive and only slightly fractured, with exploitable depths ranging from 10 up to 65 m [17]. Sustainability 2019, 11, x FOR PEER REVIEW 11 of 17
FigureFigure 14 14.. “Pietra“Pietra di di Serrenti” Serrenti” quarry in in Monte Monte Atzorcu. Atzorcu.
The most common and effective effective quarrying method is by “single slice and horizontal step”. step”. Quarrying motion motion leads leads downward, downward, using using quarry quarry cu cutterstters mounted mounted on ontracks tracks andand equipped equipped with with two toothedtwo toothed sawing sawing disks—one disks—one vertica vertically,lly, and andthe other the other one onehorizontal horizontally.ly. Cutting Cutting speed speed is about is about 1–2 2 2 1–2m/min, m/min, with with a maximum a maximum daily daily output output of ofabout about 200 200 m m2. After. After an an adequate adequate preparation preparation of of the the quarry quarry yard, parallel lines are traced on the surface of the rock slice with the verticalvertical blade. The cut is then made simultaneously by the two blades: The The vertic verticalal disk disk has has a a maximum maximum cutting cutting depth depth of of 40 40 cm, cm, which determinesdetermines thethe sizesize of of the the primary primary blocks blocks cut cut out out of theof the quarry quarry loaf loaf (maximum (maximum size: size: 40 4060 × cm,60 which determines the size of the primary blocks cut out of the quarry loaf (maximum size:× 40 × 60 cm,and and length length according according to requirements) to requirements) as shown as shown in Figure in Figure 15. 15.
Figure 15. 15.Partial Partial view view of a of quarry a quarry of red of “trachyte” red “trach excavatedyte” excavated by using the by “single using slice the and“single horizontal slice andstep” horizontal method (courtesy step” method of Primavori, (courtesy 2011). of Primavori, 2011).
Following this cutting method, other stone units as well as blocks can be obtained obtained already already during primary cuttingcutting inin thethe quarry: quarry: Solid Solid stone stone for for masonry masonry work, work, strips strips of of di ffdifferenterent thicknesses, thicknesses, or slabsor slabs for for paving applications. Strips and slabs can be obtained also in the fabrication plant, by cutting the block with a bridge sawing machine with diamond-tipped disk. During the quarrying of larger blocks, a higher step is required. Its height should be at least equal to what will be the height of the quarried blocks; in this case, more advanced technologies such as chain-cutters and/or diamond-wire cutting machines have to be used (Figure 14) Moreover, the stone deposit could have portions of rock of considerable volume which are already partially or completely detached from the rest of the rock mass; to isolate them, it is necessary
Sustainability 2019, 11, 3706 11 of 16 paving applications. Strips and slabs can be obtained also in the fabrication plant, by cutting the block with a bridge sawing machine with diamond-tipped disk. During the quarrying of larger blocks, a higher step is required. Its height should be at least equal to what will be the height of the quarried blocks; in this case, more advanced technologies such as chain-cutters and/or diamond-wire cutting machines have to be used (Figure 14). Moreover, the stone deposit could have portions of rock of considerable volume which are already partiallySustainability or 2019 completely, 11, x FOR detachedPEER REVIEW from the rest of the rock mass; to isolate them, it is necessary12 to of use 17 earthmoving machines, such as shovels and excavators. The block is safely separated, perhaps with some drillingto use earthmoving and metal wedges, machines, and such despite as shovels having and irregular excavators./non-geometric The block shapes, is safely nevertheless separated, providesperhaps significantwith some volumesdrilling fromand whichmetal itwedges, is possible and to despi producete having large slabs irregular/non-geometric dimensions, thicknesses shapes, and artifactsnevertheless of complex provides shape. significant volumes from which it is possible to produce large slabs dimensions, thicknesses and artifacts of complex shape. 3.2. Stone-Processing and Products 3.2 Stone-ProcessingSimilar to basalts and [ 18Products], the processing of “trachytes” follows different techniques, depending on the quarrySimilar availability to basalts [1 and8], thethe useprocessing of the stone of “trach material.ytes” follows different techniques, depending on the quarWhenry availabili dealing withty an ad medium-largethe use of the stone block, material. it is preferred to saw it into large slabs, obtained by meansWhen of diamond-wire dealing with plants,a medium-large multi-blade block, gangsaw, it is pr gianteferred disk to cutters. saw it into large slabs, obtained by meansSome of d ofiamond-wire the finishings plants, that multi-bl leave theade surface gangsaw, smooth giant or di semi-smooth,sk cutters. the saw-plane, the honed, the glossSome and of the finishings antiqued are that the leave more the requested. surface smooth or semi-smooth, the saw-plane, the honed, the glossBush-hammering, and the antiqued shot-blasting, are the more brushing requested. and splitting are the most popular surface finishings whichBush-hammering, have a more traditional shot-blasting, rustic appeal. brushing and splitting are the most popular surface finishings whichRegarding have a more the cut-to-sizetraditional phase, rustic thisappeal. is carried out with modern CNC cutters, often equipped with devicesRegarding that expand the cut-to-size its performance phase, andthis whichis carr canied beout used with for modern profiling, CNC shaping, cutters, lathes,often equipped and with traditionalwith devices cutters that expa (as jibnd mill its performance or bridge milling). and which can be used for profiling, shaping, lathes, and with Thetraditional production cutters of (as building jib mill or elements, bridge milling). masonry blocks and brick-sized blocks represents a segmentThe ofproduction particular importanceof building for elements, the “trachytes”; masonry these blocks are mainlyand brick-sized parallelepiped-shaped blocks represents artifacts, a usedsegment during of construction,particular importance and they arefor usedthe as“tra load-bearingchytes”; these elements are mainly in enclosure parallelepiped-shaped and containment walls,artifacts, structural used during works construction, and replacement and they restorations are used of as architectural load-bearing and elements artistic works,in enclosure as shown and incontainment Figure 16. walls, structural works and replacement restorations of architectural and artistic
(a) (b)
FigureFigure 16.16. SinkSink ( a(a)) and and clock clock (b) in(b) Ozieri in Ozieri “trachyte” “trachyte” (courtesy (court of Pedraesy Noaof Pedra di Gavino Noa Mulas di Gavino [19]). Mulas [19]). 3.3. Notes on the Wheatering of Sardinian Volcanic Calkaline Rocks 3.3 NotesThe dionff theerent Wheatering mineral composition of Sardinian (withVolcanic some Calkaline presence Rocks of glass, and some of different phenocrysts), a wideThe range different of physical mineral structure composition (due mainly (with to thesome porosity, presence density, of hardnessglass, and which some are summarizedof different inphenocrysts), Table1), can a encouragewide range the of physical process of structure decay. In(due fact, mainly the decay to the of porosity, stone depends density, on hardness the combined which actionare summarized of weathering in Table (e.g., 1), solar can radiation,encourage rainwater, the proces streams of decay. water, In carbon fact, the dioxide, decay of sulfate, stone seawater,depends duston the etc.) combined and on itsaction mineral of weathering composition, (e.g., texture solar and radiation, structure rainwater, of stone thatstream is used water, in monumentscarbon dioxide, and engineeringsulfate, seawater, structures. dust etc.) In particular, and on its themineral weathering compos ofition, volcanic texture rocks and is structure mainly due of stone to the that combined is used in monuments and engineering structures. In particular, the weathering of volcanic rocks is mainly due to the combined action of the wind with sea salt spray in Sardinia. For example, in the facies with porphiric structure and high capillary porosity (i.e., “trachytes” of Fordongianus), salt from the seawater produces new crystal growths and salt accumulation in the pore, extensive efflorescence and subefflorescence, with consequent crumbling, flaking, detached crust, color change phenomena. On the contrary, in the well compacted ignimbrites and tuffs facies, that are characterized by very low porosity and permeability (as “trachyte” of Sant’Antioco) the wheatering is very weak and no changes are visible and the stones used are very resistant to the action of atmospheric agent. Sustainability 2019, 11, 3706 12 of 16 action of the wind with sea salt spray in Sardinia. For example, in the facies with porphiric structure and high capillary porosity (i.e., “trachytes” of Fordongianus), salt from the seawater produces new crystal growths and salt accumulation in the pore, extensive efflorescence and subefflorescence, with consequent crumbling, flaking, detached crust, color change phenomena. On the contrary, in the well compacted ignimbrites and tuffs facies, that are characterized by very low porosity and permeability (as “trachyte” of Sant’Antioco) the wheatering is very weak and no changes are visible and the stones used are very resistant to the action of atmospheric agent.
Table 1. Physical and mechanical properties of some Sardinian trachytes currently on the market.
Stone Properties—UE Fordongianus UNIT Pietra di Serrenti Red Montresta STANDARDS “Trachyte” Petrographic denomination—EN Pyroclastic rock Ignimbrite Pyroclastic rock 12407:2007 Real density—EN 1936:2007 kg/m3 2,204 2290 1612 Apparent density—EN 1936:2007 kg/m3 2,688 n.a. 2662 Total porosity—EN 1936:2007 % 18.00 n.a. 39.40 Open porosity—EN 1936:2007 % 17.00 n.a. 39.20 Water absorption at atmospheric % 6.30 n.a. 21.70 pressure—EN 13755:2008 Water absorption coefficient by g/m2s0.5 23.30 n.a. n.a. capillarity EN 1925:2000 5.4–12.31 (dry Flexural strength under sample) concentrated load—EN MPa 18.90 8.20 1.63–6.871 (wet 12372:2007 sample) Flexural strength under concentrated load (after 48 MPa 15.50 n.a. not frost-resistant freeze-thaw cycles)—EN 12372:2007 + EN 12371:2003 93.2–104.51 (dry Compressive strength—EN sample) MPa 93.00 49.00 1926:2007 67.7–74.91 (wet sample) Compressive strength (after 48 freeze-thaw cycles)—EN MPa 90.10 n.a. 34.00 1926:2007 + EN 12371:2003 Resistance to ageing by thermal % n.a. n.a. ∆E = 7.9 shock—EN 14066:2004 − 1.75–1.871 (dry Abrasion resistance—EN sample) mm 25 23.00 14157:2005 1.91–2.041 (wet sample) ∆m = 0.94 Resistance to ageing by SO2 action − significant in the presence of humidity—EN % n.a. n.a. variation of the 13919:2004 color 76 (sawplane, dry Slip resistance by means of the 77 (sawplane, sample) n.a. pendulum tester—EN 14231:2004 wet sample) 63 (sawplane, wet sample) Linear thermal expansion µm/m/ C n.a. n.a. 5.94 coefficient—EN 14581:2005 ◦ Rupture energy EN 14158:2005 J 8 n.a. n.a. d = 11 d = 11,1 Breaking load at dowel hole—EN mm (d , b ) 1 1 1 A b = 49 n.a. b = 37 13364:2003 kN (F) A A F = 1.50 F = 0.86 Sustainability 2019, 11, 3706 13 of 16
3.4. Market Unlike marble and granite, whose market trend is widely documented, “trachytes” quarrying Sustainability 2019, 11, x FOR PEER REVIEW 14 of 17 (raw production) can be difficult to track down and describe [20]. In fact, the quarried “trachytes” is Europe,often sold especially locally, into otherGermany words and it doesn’tUK, and cross also theto the boundaries USA. Some of the is exported country where from Sardinia it was quarried to the Italianand processed; domesticthis market. is due to the low market value when compared to more noble varieties of marbles andStatistics granites [ 21are]. However,shown in aTable little percentage2 and Figure of Sardinian17; in Table “trachyte” 2, the production is currently trend exported of Sardinian to Europe, “trachytesespecially and to Germany tuffs” for and ornamental UK, and use also is to upward. the USA. Figure Some 16 is shows exported the from number Sardinia of active to the quarries Italian duringdomestic the market. last 25 years. ItStatistics has been are difficult shown to in evaluate Table2 andthe producti Figure 17ons; inbefore Table 19992, the because production “trachytes” trend ofand Sardinian tuffs had been“trachytes inserted and in tu theffs” group for ornamental “stones”, usewhich is upward. included Figure also sandstones 16 shows the and number basalts of in active the previous quarries statistics.during the last 25 years.
TableTable 2.2.Sardinian Sardinian “trachytes” “trachytes” and tuandffs (usedtuffs as(used ornamental as ornamental stone) offi cialstone) quarrying official production quarrying in 3 production1994–2017 (in in m 1994–2017). Elaboration (in fromm3). RegioneElaboration Autonoma from dellaRegione Sardegna Autonoma (R.A.S.) [della22] and Sardegna our own (R.A.S.)data [23 ,24[22]]. and our own data [23,24].
1994 1994 19991999 2002 2002 2005 2005 2007 2007 2012 2014–20172014–2017 3 QuarryingQuarrying Production Production [m[m]3] 21,30021,300 52405240 13,195 13,195 19,950 19,950 12,013 12,013 15,900 15,900 111,685 111,685
FigureFigure 17.17. Number of of “trachytes” “trachytes” and and tuff stuffs operating operating quarries quarries in Sardinia. in Sardinia. Elaboration Elaboration from R.A.S. from [22] and our own data [23,24]. R.A.S. [22] and our own data [23,24]. It has been difficult to evaluate the productions before 1999 because “trachytes” and tuffs had been 4. Geotourism Remarks inserted in the group “stones”, which included also sandstones and basalts in the previous statistics. Geoethical values promote the right of citizens to access and receive transparent information pertaining4. Geotourism to the Remarks intrinsic nature and meaning of geodiversity [25,26]. Geoheritage encourages the knowledgeGeoethical of the valuesnotions promote pertaining the to right the preservation of citizens to of access Earth Science and receive principles transparent [27]. information pertainingWe believe to the that intrinsic the best nature way to and represent meaning geoethical of geodiversity values and [25 ,geoheritage26]. Geoheritage is the organization encourages theof aknowledge tour of historical of the notionstowns and pertaining archaeological to the preservation sites where Sardinian of Earth Science different principles types of [27“trachyte”]. have been used.We believe This info-tour that the bestshould way be to followed represent by geoethical the visit to values historical and geoheritagequarries of “trachytes” is the organization as well as of thosea tour quarries of historical which towns are still and fully archaeological operational. sites The wheretours will Sardinian be led by diff qualifiederent types scientific of “trachyte” guides with have abeen degree used. in geoheritage This info-tour topics. should be followed by the visit to historical quarries of “trachytes” as well as those quarries which are still fully operational. The tours will be led by qualified scientific guides with 4.1.a degree A possible in geoheritage Example: Bosa topics. Heritage Stone Tour Bosa is a municipality built from a medieval town on the western coast of Sardinia (see Figure A Possible Example: Bosa Heritage Stone Tour 1). This municipality received a tourism award as Italy's second most attractive town in 2014 (tourism awardBosa ‘I borghi is a municipality più belli d’Italia’ built from[28]). a Our medieval proposal town consists on the of western a walking coast tour of Sardinia to view (seea number Figure 1of). monumentsThis municipality which receivedwere built a tourism using the award local as Bosa Italy’s “Trachyte” second most (Figure attractive 13(7)) townsuch inas 2014the castle (tourism of Serravalle—i.e., a XIII century fortification that dominates the town of Bosa from above—and the Church of San Pietro extra muros (already shown in Figure 4b). The tour shall end at the historical quarry “sas Pedraggias”. It shall consist of about 6 km and last for about 4 hours. For the above mentioned sites, see Figure 18.
Sustainability 2019, 11, 3706 14 of 16
award ‘I borghi più belli d’Italia’ [28]). Our proposal consists of a walking tour to view a number of monuments which were built using the local Bosa “Trachyte” (Figure 13(7)) such as the castle of Serravalle—i.e., a XIII century fortification that dominates the town of Bosa from above—and the Church of San Pietro extra muros (already shown in Figure4b). The tour shall end at the historical quarry “sas Pedraggias”. It shall consist of about 6 km and last for about 4 hours. For the above
Sustainabilitymentioned 2019, 11 sites,, x FOR see PEER Figure REVIEW 18. 15 of 17
FigureFigure 18. 18. AerialAerial view view ofof Bosa Bosa and and location location of principal of principal monuments monuments and historical and “trachyte”historical quarry “trachyte”for the hypotheticalquarry for the Bosa hypothetical heritage stone Bosa tour heritage (from Google stone Earth). tour (from Google Earth).
5. Conclusions5. Conclusions SardinianSardinian pyroclastic pyroclastic rocks, rocks, which which are generally are generally called called Sardinian Sardinian “trachytes” “trachytes” are stones are stones which which are are widespreadwidespread in the in western the western part partof Sardinia: of Sardinia: These These kinds kinds of stone of stonewere wereused usedto build to builda lot of a lotworks of works that that havehave featured featured the Island’s the Island’s history, history, from from its prehis its prehistorytory (as witnessed (as witnessed by “domus by “domus de janas” de janas” and nuraghi), and nuraghi), to theto modern the modern age, age,via the via Roman the Roman and medieval and medieval ages. ages. DuringDuring the thelast last twenty twenty years, years, the the use use of of Sard Sardinianinian “trachytes” has increasedincreased duedue not not only only to to fashion, fashion,but alsobut foralso the for restoration the restoration of a highof a numberhigh number of civic of centers civic centers in several in several municipalities municipalities throughout throughoutthe island. the island. UsingUsing commodity-related commodity-related terms, terms, Sardinian Sardinian “trachyt “trachyte”e” can show can showdifferent diff erentcolors colorsfrom the from pale the pale yellowyellow to the to thered redthrough through to pinkish, to pinkish, the green the green and andthe dark the darkgrey greyand has and different has diff erentmechanical mechanical characteristics.characteristics. It is a It fairly is a fairly cohesive cohesive rock rockand sh andows shows remarkable remarkable elements elements of aesthetic of aesthetic value valuethat have that have favored,favored, its popularity its popularity as a building as a building resource resource and ornamental and ornamental stone in stone Sardinia. in Sardinia. At present,At present, Sardinian Sardinian “trachyte” “trachyte” is very ismuch very demanded much demanded for its compactness, for its compactness, homogeneity, homogeneity, color and colorbecause and of because its easy ofworkability; its easy workability; it is usually itutilized is usually for flooring, utilized covering, for flooring, blocks covering, for open-face blocks for constructionsopen-face and constructions buildings as and well buildings as for architec as welltural as for and architectural street furnishing and street elements. furnishing All this elements. is highlightedAll this isby highlighted the growing by production the growing in the production island. in the island. ExactlyExactly for the for above-mentioned the above-mentioned reasons, reasons, it is ne itcessary is necessary to raise to raiseawareness awareness of people of people about aboutthe the diversity,diversity, the history the history and use and of use Sardinian of Sardinian “trachytes” “trachytes” through through guided guided tours. tours.
Acknowledgments:Author Contributions: The Conceptualization,Authors wish thank N.C.; investigation,to Dr. Anto S.M.G.;nio Dessena resources, for N.C. his and support S.M.G.; datain the curation, cartographicN.C.; writing—original elaboration. draft preparation, N.C. and S.M.G.; supervision, N.C.; funding acquisition, N.C. AuthorFunding: Contributions:This research conceptualization, received no external Nicola funding. Careddu; investigation, Silvana Maria Grillo.; resources,Acknowledgments: Nicola CaredduThe Authors and Silvana wish thank Maria to AntonioGrillo.; Dessenadata curation, for his support Nicola in Careddu.; the cartographic writing— elaboration. original draft preparation, Nicola Careddu and Silvana Maria Grillo.; supervision, Nicola Careddu.; funding acquisition, Nicola Careddu Funding: This research received no external funding Conflicts of Interest: The authors declare no conflict of interest.
References
Sustainability 2019, 11, 3706 15 of 16
Conflicts of Interest: The authors declare no conflict of interest.
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