Slate industry in Spain

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Los Marcos, Alcontar LosMarcos.jpg
Los Marcos, Alcóntar

90% of Europes's natural slate used for roofing originates from the slate industry in Spain, [1] with the region of Galicia being the primary source of production.

Contents

Slate is a fine-grained metamorphic rock that splits into thin, smooth-surfaced layers. Metamorphic rock is rock which was once igneous or sedimentary and has been subsequently subjected to heat and pressure in varying degrees thereby altering its composition, structure and appearance. It is used extensively in the building industry, particularly for roofing tiles. The production of slate is estimated at 4 million tons per year. [2]

Geography of Galicia

Galicia is situated on the North West coast of Spain, just above Portugal, and is subdivided into the four provinces of A Coruña, Pontevedra, Lugo and Ourense.

The main areas of slate production are:-

Early history of Galicia

The early history of the region has been shaped by a variety of key cultures and influences:-

4500 – 1500BC The Megalithic culture was the first major influence in the region. They were noted for their skills in construction and architecture, and the remains of thousands of tombs (or dolmens) can be found in the region.

1500 – 700BC There was a substantial increase in trade with the rest of Europe during the Bronze Age, prompted largely by developments in metallurgy.

800 – 500 BC During this period the region was heavily influenced by Celtic culture, and caestros (circular fortified areas atop a hillside, surrounded by a moat) became a common sight.

137BC The first Roman to enter the area was Decimus Junius Brutus.

410AD Galicia fell to the Suevi ( or Suebi) German tribe, following the fall of the Roman Empire, and they formed the first post Roman medieval kingdom in Europe.

584AD Galicia was invaded by the Visigothic King Leovigild

711 – 718AD The Moors attempted to gain control over Galicia, as they had done the rest of Spain, but with little success.

739AD The Moors were defeated by Alfonso I of Asturias and Galicia became integrated into the kingdom of Asturias

835AD Relics said to originate from the Apostle St James (James, son of Zebedee) were discovered in Santiago de Compostela, and the area became one of the most important pilgrimage sites in the Christian world. This remains one of the heritage sites for which the region is renowned even today.

Spanish slate geology

Slates and Echinospartum in Teleno, Corporales, Leon, Spain El Teleno pizarras.jpg
Slates and Echinospartum in Teleno, Corporales, León, Spain

The Northern region of Spain has been subjected to periods of magmatic activity with volcanism, and this has led to the region's unique geological development in respect of slate.

Slate deposits are over 500 million years old, having been formed during the Cambrian, Ordovician and Silurian periods of the Palaeozoic era.

Essentially, slate forms when the clay minerals in shale are put under increased pressure with high temperatures. The clay starts to revert to the mica minerals which cause the rock to grow hard with pronounced cleavage) directions. It is this cleavage which enables slate to be broken along flat, even planes.

A large variety of colours and textures of slate can be produced, and the final product depends largely on the tectonic environment, the source of the sedimentary material, and the physical/chemical conditions prevalent during the sedimentation process.

As the sedimentary deposits were compacted, water was squeezed out, hence turning clay minerals into mica, and then solid mudstone. The subsequent mountain building compaction which occurred over the next few million years resulted in an even stronger rearrangement and planar orientation of the minerals. This means that in true slate the cleavage plane is very different from the original bedding plane [4] and led to the well developed cleavage for which the region is famous. [5]

Extraction of Spanish slate

The Galician slate industry is a major employer in the region and in the main slate is extracted from surface quarries. The process is as follows: [6]

  1. Geological surveys locate areas of potential slate extraction
  2. Samples are taken to allow the purity and quality of the slate to be verified.
  3. The quarry area is established, and any unusable material (“overburden”) is removed.
  4. Diamond beaded steel cutting cables are used to saw large blocks from the quarry.
  5. These blocks are transferred to the production centre to be sawn into regular smaller blocks, using their natural cleavage planes.
  6. Skilled craftsmen grade the blocks according to quality and thickness, after having split them to a predetermined size.
  7. After final quality control measures, slates are packed into crates, often with batch information so that future matches will be possible for longer term ongoing projects.

Properties of Spanish slate

Since slate is a naturally occurring product, different kinds of slate are subject to varying chemical and mineral compositions, determined largely by the geological characteristics of the quarry from which it was mined. [7]

An important use of Spanish slate is as a roofing material, often being specified by building professionals as a result of its aesthetic appearance and durability characteristics. Slate is particularly suitable as a roofing material as it has an extremely low water absorption index of less than 0.4%. Its low tendency to absorb water also makes it very resistant to frost damage and breakage due to freezing.

Slate certification

Laminations due to alternating layers of limonite and mudstone Scale x25 Laminating layers.jpg
Laminations due to alternating layers of limonite and mudstone Scale x25
No laminations present in layers with a high quartz and feldspar content Scale x 25 Non laminated.jpg
No laminations present in layers with a high quartz and feldspar content Scale x 25

The nature of slate as a natural organic product results in a wide variety of qualities being available worldwide. An important way of determining the differences, and degree of quality, is through the use of country certification, or quality marks.

The CE mark certifies that a product has met the EU requirements for consumer safety, health and environmental issues. [8] All Spanish Slate bears this mark.

There are further national and international standards that can be applicable to slate, and give information as to the quality levels reached. Some of these are:-

Using Spanish slate on roofs

Typically Spanish slate tiles are fixed using a hook fixing method, as opposed to the more predominant nail fixing used elsewhere in the world. The benefits of hook fixing are [11]

Environmental implications

Dr Joan Walsh, a consultant geologist, writes in her article “Natural Slate: a Green Roofing Medium”, [12] that natural slate offers strong benefits over other roofing materials in terms of carbon emissions and reduced environmental impact.

In addition, the quarrying of Spanish slate does not involve any chemical processes, and usually only local water is used to keep cutting machinery cool.

After quarrying regional authorities often dictate that the landscape is returned as much as possible to its original state, and waste rock left as part of the extraction process is returned adjacent to the quarry. But often waste rock is abandoned near small villages, riversides or even burying many historical heritage sites. [13] [14]

Related Research Articles

<span class="mw-page-title-main">Galicia (Spain)</span> Autonomous community in the northwest of Spain

Galicia is an autonomous community of Spain and historic nationality under Spanish law. Located in the northwest Iberian Peninsula, it includes the provinces of A Coruña, Lugo, Ourense, and Pontevedra.

<span class="mw-page-title-main">Slate</span> Metamorphic rock

Slate is a fine-grained, foliated, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade, regional metamorphism. It is the finest-grained foliated metamorphic rock. Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression.

<span class="mw-page-title-main">Quarry</span> A place from which a geological material has been excavated from the ground

A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to reduce their environmental impact.

<span class="mw-page-title-main">Tile</span> Manufactured piece of hard-wearing material

Tiles are usually thin, square or rectangular coverings manufactured from hard-wearing material such as ceramic, stone, metal, baked clay, or even glass. They are generally fixed in place in an array to cover roofs, floors, walls, edges, or other objects such as tabletops. Alternatively, tile can sometimes refer to similar units made from lightweight materials such as perlite, wood, and mineral wool, typically used for wall and ceiling applications. In another sense, a tile is a construction tile or similar object, such as rectangular counters used in playing games. The word is derived from the French word tuile, which is, in turn, from the Latin word tegula, meaning a roof tile composed of fired clay.

<span class="mw-page-title-main">Dimension stone</span> Natural stone that has been finished to specific sizes and shapes

Dimension stone is natural stone or rock that has been selected and finished to specific sizes or shapes. Color, texture and pattern, and surface finish of the stone are also normal requirements. Another important selection criterion is durability: the time measure of the ability of dimension stone to endure and to maintain its essential and distinctive characteristics of strength, resistance to decay, and appearance.

<span class="mw-page-title-main">Carballo</span> Municipality in Galicia, Spain

Carballo is a municipality in the north western region of Spain in the province of A Coruña, in the Autonomous community of Galicia, Spain and seventeenth overall in the country. It belongs to the Comarca of Bergantiños.

<span class="mw-page-title-main">Minho (river)</span> River in Spain, Portugal

The Minho or Miño is the longest river in Galicia, sharing the border with Portugal, with a length of 340 kilometres (210 mi). By discharge, it is the fourth river of the Iberian peninsula, after the Douro, Ebro, and Tagus.

<span class="mw-page-title-main">Slate industry</span> Industry of the extraction and processing of slate

The slate industry is the industry related to the extraction and processing of slate. Slate is either quarried from a slate quarry or reached by tunneling in a slate mine. Common uses for slate include as a roofing material, a flooring material, gravestones and memorial tablets, and for electrical insulation.

<span class="mw-page-title-main">El Bierzo</span> Comarca in Castile and León, Spain

El Bierzo is a comarca in the province of León, Spain. Its capital is the town of Ponferrada. Other major towns are Bembibre and Villafranca del Bierzo, the historical capital.

<span class="mw-page-title-main">Yorkstone</span> Variety of sandstone from Yorkshire, England

Yorkstone or York stone is a variety of sandstone, specifically from quarries in Yorkshire that have been worked since the middle ages. Yorkstone is a tight grained, Carboniferous sedimentary rock. The stone consists of quartz, mica, feldspar, clay and iron oxides.

<span class="mw-page-title-main">Galician wine</span>

Galician wine is Spanish wine made in the autonomous community of Galicia in the northwest corner of Spain. It includes wine made in the provinces of A Coruña, Ourense, Pontevedra and Lugo. Within Galicia are five Denominacións de Orixe (DO): Monterrei, Rías Baixas, Ribeira Sacra, Ribeiro and Valdeorras. In recent years, the region has seen a resurgence in its wine industry led by the international acclaim being received by the Rías Baixas region for its Albariño wines.

<span class="mw-page-title-main">Roman walls of Lugo</span> Defensive fortification in Lugo, Spain

The Roman walls of Lugo are the ancient Roman defensive walls stretching 2,120 metres (6,960 ft) around the Old Town of Lugo, Spain. They were built in the third century AD to defend the ancient Roman town of Lucus Augusti. The fortifications, still largely intact, were declared a UNESCO World Heritage Site in 2000 and are a popular tourist attraction.

<span class="mw-page-title-main">As Catedrais beach</span>

Praia das Catedrais is on the northwest coast of Spain. It is the name given by the tourism industry to Praia de Augas Santas. The beach is located in the Ribadeo municipality, in the province of Lugo (Galicia), on the Cantabric coast, and it lies about ten kilometres to the west of the town of Ribadeo. Its name is derived from its cliff formations.

<span class="mw-page-title-main">Galician culture</span> Culture and traditions of Galicia, Spain

The culture of Galicia is the patterns of human activity and symbolism associated with the Galicia region of Spain and the Galician people.

<span class="mw-page-title-main">Galician Massif</span>

The Galician Massif is a system of mountain ranges in the northwestern corner of the Iberian Peninsula. It is located in Galicia with its southeastern end reaching into the provinces of Zamora and León of Castile and León. Its highest point is Pena Trevinca at 2,127 metres (6,978 ft). Another important peak is Cabeza de Manzaneda.

Julio Díaz Sánchez is a Spanish football coach and former player.

<span class="mw-page-title-main">Galicia and World War II</span> Aspect of history

The participation of Galicia (Spain) in World War II was marked by its location on Spain's Atlantic coast. Despite Spain's neutrality in the war, the country was affected due to its strategic location. The tungsten mines, such as the Mines of San Fins, were used for the Axis war industry. The extraction and transport of the mineral carried out by front companies, such as the Finance and Industrial Corporation.

<span class="mw-page-title-main">Parc quarry</span> Disused slate mine in North Wales

Parc Quarry was a compact underground slate quarry in the Croesor Valley, Gwynedd, North Wales. It was connected to the Croesor Tramway, which ran through the valley. The quarry concentrated on producing specialist slate products, rather than roofing slates, and was managed for much of the time by the innovator Moses Kellow. It operated for about 50 years, from 1870 to 1920.

<i>Galicia irredenta</i> Term used for the Galician-speaking territories outside of Galicia

Galicia irredenta or Galicia estremeira, also spelled as Galiza irredenta and Galiza estremeira and also known as Faixa Leste or Franxa Leste, is a term used for all Galician-speaking territories located outside of Galicia. These are all located in Spain, in either Asturias or Castile and León. These territories are sometimes divided into three subregions: El Bierzo, Eo-Navia and As Portelas.

References

  1. European Association of Mining Industries website Archived 2010-01-30 at the Wayback Machine retrieved on 26/01/2010
  2. Fundación Centro Tecnológico de la Pizarra’s report into the ’Technical properties of Bambui Slate from the State of Minas Gerais (Brazil) to ascertain its compliance with the Standard EN12326’ Brazilian Slate Report summarized by Consultant Geologist J A Walsh Archived 2009-12-29 at the Wayback Machine , retrieved on 27/01/2010
  3. 1 2 3 4 AGP Galician Slate Association Regional production retrieved on 26/01/10
  4. Page 3 Positioning Systems for Slate Roofs retrieved on 26/01/10
  5. Galician and Spanish Slate website Geology Archived 2010-02-04 at the Wayback Machine retrieved on 26/01/10
  6. Galician and Spanish Slate website Slate Extraction Archived 2010-02-04 at the Wayback Machine retrieved on 26/01/10
  7. 1 2 3 4 Galician and Spanish Slate website Quality Archived 2010-01-31 at the Wayback Machine retrieved on 26/01/10
  8. CE mark certification Archived 2008-12-01 at the Wayback Machine retrieved on 26/01/10
  9. Official website for the NF Mark of France retrieved on 26/01/10
  10. AFNOR Group website Certification retrieved on 26/01/10
  11. Galician and Spanish Slate website Hook fixing Archived 2010-01-23 at the Wayback Machine retrieved on 26/01/10
  12. Page 4 Natural Slate: a Green Roofing Medium by Dr Joan Walsh, retrieved 26/01/10
  13. Galician and Spanish Slate website Ecology Archived 2010-02-06 at the Wayback Machine retrieved on 26/01/10
  14. Tempos Novos 263, A montaña rachada, pp.27-30