Calcites from Pedreira do Vidro Quarry, PortugalLast Updated: 15th Jan 2015
By Rui Nunes
Calcites from Pedreira do Vidro Quarry
Pedreira do Vidro Quarry (PVQ), Moita do Poço, Turquel, Alcobaça, Leiria District, Portugal
Moita do Poço is a small place whose age is lost in the dust of time, in the foothills of the Serra dos Candeeiros, where people live in healthier air of the smell of rosemary and still in a certain bucolic landscape. People lived until a few decades ago of grazing, mining and extraction of stone. Still today the extraction of limestone is strongly established.
PVQ was my first mineralogical location in the days when I thought that the calcite was nothing more than rhombs. I still remember when this quarry was discovered by me in a cold and foggy morning which gave it a certain mystery... Over the years I visited PVQ many times and gathered hundreds of fine specimens.
Calcites with some different colors were not very common in other quarries scattered throughout the region of Alto da Serra; it either had a caramel color, or a gray translucent ... picked up many floating and twins, specimens of spectacular and unexpected shapes.
From what I know, PVQ is the largest surface calcite concentration in Portugal.
I could not get much information about its golden age. There are some records of the early activity of a calcite quarry in 1973 and its closure in 1978.
I think that PVQ was to be considered to be of geological interest since they are still vestiges of a perimeter fence and wooden stairs leading to the deepest part of the quarry. I got to hear something about this...
Some unscrupulous visitors broke large crystals and vandalized many of the existing huge holes. It is even difficult to find good specimens in the present days. But PVQ still has its charm and after a few minutes of contemplation and if we focus our attention somewhere in its walls and with some luck we still can find a place that can offer us a good specimen.
Be careful as PVQ is a somewhat dangerous local with unexpected landslides.
For a better understanding of the whole environment surrounding PVQ I refer some aspects and curiosities that I think of interest in general.
PVQ is located in the Serra dos Candeeiros (also known as Serra dos Albardos).
"Serra dos Candeeiros begins in the Arrimal´s parish and extends southwest for about 22 km below Rio Maior. Also called Serra dos Molianos, Alcobertas, Rio Maior. It has a maximum altitude of 485 m and the spaced vegetation that covers it reflects the calcareous/limestone nature of the area.
With Serra de Aire, the massif of Porto de Mós, mountain group in the western seafront - new area of relief that, with Iberian Meseta (Meseta Ibérica), the southern coastline and the lower basins of the Tagus and Sado, forms one of the four principal national relief zones. As this mountain range that runs from the outskirts of Porto de Mós to Rio Maior, can be considered the eastern boundary of the vast region, which was the “hunting grounds” of Alcobaça, according to a study by Pinho Leal, its etymology "Albardos, from Arabe which means something cold".
Serra dos Candeeiros is composed by limestones dating from the Middle Jurassic to the Upper Jurassic is the most important Portuguese limestone massif. Tectonic phenomena slowly create caves and aquifers existing along Serra dos Candeeiros. The west side, area of Jurassic and Cretaceous hills, has a slightly wavy relief, and is deformed by valleys and ravines.
In "Joaquim Vieira Natividade, Região de Alcobaça, imp Líbano, Lisboa, s/d pag 19".
Serra dos Candeeiros is also known for its impressive natural caves and it is located in the Natural Park of Serra de Aire e Candeeiros. This Natural Park is a protected area established in 1979 and aims at the protection of natural features as well as protecting the existing architectural heritage in the Serras de Aire e Candeeiros, has a large area including the municipalities of Alcobaça and Porto de Mós in the Leiria district and Alcanena, Rio Maior, Santarém, Torres Novas and Ourém in the Santarém district.
The Park is framed in the Maciço Calcário Estremenho, covering the two mountains that give the name and even the plateau of Santo Antonio and the plateau of São Mamede.
Derived from tectonic movements and the modulation of the ground, these units are delimited by geological units resulting from the formation of failure: depression of Alvados, Mira-Minde Poljes and depression of Mendiga. The area covered by the Park is in a state of transition between Atlantic and Mediterranean influences. Due to the large number of caves and other rock cavities it is not surprising that there are in there some protected species of bats.
The stone is an ever-present in the landscape of the Natural Park of Serra de Aire e Candeeiros which occupies more than two-thirds of Maciço Calcário Estremenho (Massif in Mesozoic limestone) which is the most important limestone area of Portugal. Over time, through geo-morphological processes, the natural elements have been shaping the mainly calcareous rock, giving rise to more than one thousand and five hundred caves.
The Massif, like any mountain formation, originated in the tectonic movements of the earth's crust, after thousands of years of movement of continental and oceanic plates, the surface has emerged: the Minde Polje, Alvados, Mendiga and the Arrimal Dolina. A large part of the existing geological structures had their origin in the Middle Jurassic. Other, more recent origin, are composed by debris and sedimentary materials. It is also worth mentioning the presence of Terra Rossa, particularly in areas of depression.
Another interesting place are the old Salt Pans of Rio Maior considered a natural phenomenon in the Park - at about 30 km from the Atlantic sea. The water from this spring is seven times more salty than the sea water: 1 liter of salt water = 220 grams of solid salt. Though the oldest document that refers to salt pans is dated 1177 it is believed that the use of rock salt was done since prehistoric times.
The water, barely visible on the surface, is abundant in the subsoil, making this area one of the greatest, or even the largest underground reservoir of freshwater in the country, this reservoir is going from Leiria to Rio Maior, is fed mainly by rain, infiltrating rapidly, forming underground rivers, after returning the surplus to the surface, forming a karst spring as is the case the source of the Olhos de Água do Alviela, the most important of all funding and target for water supply to Lisbon since 1880.
In the area of Natural Park of Serra de Aire e Candeeiros are identified more than 1,500 karst cavities, resulting from water infiltration through cracks and diaclases and subsequent action on the chemical weathering of limestone. This process results in a vast and complex network of underground rivers that is emerging galleries horizontal development (caves) and vertical development of natural wells (algares). The water that flows in these galleries, eventually depositing limestone precipitates, causing a variety of speleothems that translate into forms of great beauty as stalactites, stalagmites, columns, and calcite mantles.
There are many interesting places in the region; I highlight three:
1. some Caves open to the public in Mira de Aire, Serra de Santo António and Alvados - the soil characteristics of the region allowed the formation of giant and fantastic underground caves;
2. the Natural Monument of Dinosaur Footprints from the Serra de Aire, known only by Footprints of the Serra de Aire was established in 1996 and is situated in the Ourém municipality. The tracks were discovered on 1994 in an active limstone quarry locally named Pedreira do Galinha. It features 20 tracks of sauropods, which are aged 175 million years. Sauropod tracks are the largest, oldest and sharpest known;
3. and the Minde Polje which was included in 2005 on the List of Wetlands of International Importance. It is a karstic depression that in years of heavy rain is flooded for several months.
Much more could be reported about this nice region of Portugal. It is true that good friends who visit us always come back ... Dear reader of this article, you will be welcome too! Feel free to contact me if you need further or more detailed information.
It is this complex of limestone geomorphologic features that set the limits of the Natural Park of Serra de Aire e Candeeiros.
From the morphological point of view in this massif three distinct areas can be difered: Serra dos Candeeiros in the west, Santo António Plateau, center and south, and the São Mamede Plateau and Serra de Aire, the north and east, respectively.
 Terra Rossa: a type of very fertile purple soil which is the result of millions of years of decomposition of basaltic rocks.
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