Porphyry informations

Historical evolution

Porphyry is a volcanic, eruptive rock which got cold out of the earth's crust 260 millions of years ago. The use of porphyry for monolithic monuments is known since the earliest times. The discovery of stratified porphyry, that is to say with natural surface, dates back to the last decades of the 17th century. The two natural surfaces permit to cut four faces instead of six and the superior area with his natural quarry surface has a natural roughness instead of a cut one. In the end of 1800Scandinavian workers, used to cut manually granite cubes, came in Trentino to work in the quarries and begun a production of cubes for streets paving. Before than, this stratified porphyry was only used to cover roofs or for building. The first considerable street pavings begun in the ’30, but only after the second world war started an important development in mechanization.

Applications

Porphyry is an extrusive ignimbrite characterised by a sub-vertical slab-like structure with parallel strata. Because of this natural stratification it is necessary to use explosives to quarry the slabs. The explosion causes the fall of the material which will be sorted out according to the sizes and the thickness of the pieces. It is not selected according to the colour which is very varying as a result of thousands of years of moisture, oxides and concretions infiltrations which caused a range of colours going from grey to red and violet with many nuances. The main chemical components of porphyry are silicon, aluminium, potassium, iron, calcium and sodium. Among the mineralogic ones there are quartz, sanidine and plagioclase. This composition makes of porphyry one of the most important materials both for paving and for cladding and one of the strongest stones. Porphyry stands wear and tear very well, it is resistant to ice and intense cold and to all atmospherical agents. Thanks to its chemical and physical features it is suitable for the collocation of pedestrian areas, carriageable streets and for areas subject to heavy traffic. Porphyry great qualities and in particular its chromatic variety and its anti-slip guarantee, even in wet or icy conditions, allow the paving of streets, squares, courtyards, historical centers, pedestrian areas, gardens, parks and the creation of street furniture items. It is very suited both for interior pavings and for wall facings. Porphyry is a stone which exalts architects’ and planners’ imagination giving them the opportunity to create real “works of art” thanks to its various typologies and colours.