Stones of Portugal Episode-6
Travel through the Granite of Portugal
Granite as known belongs to a larger family of rocks that have a major chemical composition of quartz and feldspars. Muscovite, Biotitic or Amphiboles are the mineral characteristics of granite rocks.
The Portuguese granites are known for their quality and variety. The frequency of their usage is on the rise. The North and Centre of the Portuguese territory are characterized by extensive areas of granitic outcrops of Palaeozoic age. These areas are associated with several mining districts of ornamental stones. Also, mining of resources for ornamental purposes takes place in the Alentejo and Algarve regions. The potentialities are mainly associated with granites of Variscan Orogeny time period.
Portuguese granites show a wide variety of colours and textures. Nevertheless, the vast majority have grey to bluish grey colours and fine to coarse granular textures, sometimes porphyroid.
These kinds of granites are exploited in most of the mining sites and among them are Pedras Salgadas and Alpendorad. These two kinds are the commercial varieties.
Its peculiarities include colour and texture and other varieties to look for the Favaco for its dark grey colour. It is found in the restricted place of the Monforte – Campo Major mining district. The Cinzento de Alpalhão, mined at Alpalhão is known for its homogeneous fine-grained texture. The Cinzento de Monchique comes from the igneous mass with the same name in the Algarve region. This variety is actually a medium to coarse grain nepheline syenite with a greyish colour in general. Reddish brown grain of the nephelometer stands out from its acicular texture.
These Grey granites are very common in the international market for ornamental stones. Granites of higher variety with good economic value stand out with pinkish or yellowish colours.
The pinkish varieties occur in the Monção and Monforte - Campo Major mining districts, where the quarries often exceed 30 m in depth, keeping with what has been mentioned for the greyish granites.
The varieties exploited here feature a coarse to very coarse grain size and are known as Rosa Monção and Rosa Monforte, respectively. Yellowish varieties are intensively exploited at several sites but the most active are those of Ponte de Lima, Mondim de Basto and Falperra. Their colour is the result of shallow weathering phenomena affecting the grey underlying granites. This particular genetics of the yellow granites justifies the values obtained for its physical-mechanical properties, when compared with those of other granite varieties.
As a result of the geological diversity that characterizes its territory, Portugal produces a large chromatic and textural variety of granites and marbles for ornamental purposes. The most abundant varieties are the greyish coloured ones which in the present day have relatively low economic value due to strong competition for this kind of stones in the global market.
Granite is hard and tough, and therefore it has gained widespread use as a construction stone.
There are several types of Granite in Portugal. From blue blue to pink, from yellow to black, the variety of granite is wide
Blue Granite: Alpendorada which is similar to the grey one.
Yellow Granite: Mondim, Vila Real, Alpendorada, Ariz, Cinfaes and Guimaraes
Macheado ( mix of yellow and blue)
Grey Granite: Alpendorada , Ariz, Lapa, Pedras Salgadas, Penafiel, Granja/ Fine grain, Pinhel , Penalva, Alpalhao, Guimaraes/ Crystal, Castro Daire, Evora and Antas
Black Granite: Roriz, National, Favaco, Angola, Zimbabwe and Impala
Pink Granite: Porrinho, Monaco and Monforte.
Ref: Helio & Monteiro LDA