The Codex Diplomaticus of Tola indicates that a church dedicated to St. Geminianus, belonging to the Camaldonese monastery of St. Geminianus of the island of Montecristo, existed in the town of Samassi starting from 1119 AD. However, the current form of the church cannot be ascribed to that period and it is thought that it was rebuilt in the late XII century or early XIII century on the ruins of an older Palaeochristian and Vandalic building. The church has a single nave, with the apse directed to the south-east. In the main façade and in those sides, the structural framework consists of a inclined skirting board, wide corner pillars, flat pilasters, and small arches with geometric and moulded decoration. The façade, with arches parallel to the pediment, supports the campanile and contains a portal with lintel on phytomorphic capitals and an arch set on anthropomorphic protomes. The walls are made of medium-sized vulcanite ashlars. These volcanic rocks, with dacitic to rhyo-dacitic composition, belonging to the Oligocene-Miocene volcanism that occurred between 33 and 11 My ago in Sardinia, present a porphyritic structure (porphyritic index 10÷20%) with phenocrysts of opaque minerals (magnetite and/or titanomagnetite), plagioclase, ± orthopyroxene, ± biotite and rare hornblende and quartz. The decay processes are distributed differently in the façades, being concentrated mainly on the basal and top parts where water circulates. There are diverse macroscopic forms of alteration and degradation: exfoliation, pitting, alveolation, decohesion, differential degradation, crypto-florescence (gypsum), etc. Traces of pinkish to honey-yellow Ca-oxalate films were found on the stone surfaces. Preliminary XRD data and polarizing microscope observations revealed at least two types of films. A survey of their distribution on the different architectonic elements is currently in progress in an attempt to clarify their precise roles.
The stones of the medieval ‘San Mamiliano di Simassi’ church (SW Sardinia, Italy): characterization and state of conservation
COLUMBU, STEFANO;GARAU, ANNA MARIA;MARCHI, MARCO;
2008-01-01
Abstract
The Codex Diplomaticus of Tola indicates that a church dedicated to St. Geminianus, belonging to the Camaldonese monastery of St. Geminianus of the island of Montecristo, existed in the town of Samassi starting from 1119 AD. However, the current form of the church cannot be ascribed to that period and it is thought that it was rebuilt in the late XII century or early XIII century on the ruins of an older Palaeochristian and Vandalic building. The church has a single nave, with the apse directed to the south-east. In the main façade and in those sides, the structural framework consists of a inclined skirting board, wide corner pillars, flat pilasters, and small arches with geometric and moulded decoration. The façade, with arches parallel to the pediment, supports the campanile and contains a portal with lintel on phytomorphic capitals and an arch set on anthropomorphic protomes. The walls are made of medium-sized vulcanite ashlars. These volcanic rocks, with dacitic to rhyo-dacitic composition, belonging to the Oligocene-Miocene volcanism that occurred between 33 and 11 My ago in Sardinia, present a porphyritic structure (porphyritic index 10÷20%) with phenocrysts of opaque minerals (magnetite and/or titanomagnetite), plagioclase, ± orthopyroxene, ± biotite and rare hornblende and quartz. The decay processes are distributed differently in the façades, being concentrated mainly on the basal and top parts where water circulates. There are diverse macroscopic forms of alteration and degradation: exfoliation, pitting, alveolation, decohesion, differential degradation, crypto-florescence (gypsum), etc. Traces of pinkish to honey-yellow Ca-oxalate films were found on the stone surfaces. Preliminary XRD data and polarizing microscope observations revealed at least two types of films. A survey of their distribution on the different architectonic elements is currently in progress in an attempt to clarify their precise roles.
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