Roofing slates of the world part III

Images of hand specimens and thin sections of slates from several world´s locations. Real color of the specimens may vary with respect of shown in the images.

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13. Slate from Penrhyn, Wales, UK. This slate is extracted at the historic quarry of Penrhyn, and is very popular in historical buildings all over the UK. The green spots correspond to zones with reduced iron and high contents of Ca and Mg (Borradaile et al. 1990). This color change can be seen in the microphotograph of 200 microns.

14. Carbonate slate from Liguria, Italy. The Liguria slates have carbonate content (see microphotograph of 500 microns) of about 20%. However, this fact does not mean that these slates are more susceptible to weathering than other slates with carbonate contents much lower. The key factor is the specific mineralogy of the carbonate. This slate complies with the EN 12326 requirements, and constitutes a perfect material for roofing when used properly. Sample provided by Euroslate.

15. Slate from Benuza, Castilla y León, Spain. An Ordovician slate, fine-grained with some cubes of pyrite, with smooth surface and dark color. This is a classic roofing slate, i.e., a slate from the green schists facies made of quartz, chlorites and mica. Sample provided by Cupa Pizarras S.A.

16. Slate from Hubei province, China. Fine-grained slate, light colored with a marked tendency to acquire a reddish aspect which makes it very interesting for special cases, since this reddish does not seem to generate rust trails. Sample provided by the Laboratorio del Centro Tecnológico de la Pizarra.

17. Green phyllite from Lugo, Spain. This Cambrian phyllite is also a very special roofing slate, being used for some singular buildings such as the Shizuoka Convention Arts Center in Japan. It is quarried in several colors ranging from grey to green. This is the Verde Xemil variety. Sample provided by Pizarras Ipisa.

18. Slate from Villar del Rey, Badajoz, Spain. A very fine-grained slate with some pyrite cubes and a dark color, in fact this is the darkest slate quarried in Spain due to its content in graphite, up to 2%.  Sample provided by Pizarras Villar del Rey, S.A.

And please remember: There are no bad slates but bad uses. The slate should be used in accordance with the building and environment requirements, so it is critical to know and understand the rock we are dealing with.

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Roofing slates of the world, part II

Images of hand specimens and thin sections of slates from several world´s locations. Real color of the specimens may vary with respect of shown in the images.

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7 – Slate Valentia, Ireland. This is a coarse-textured gray slate, with no or few iron sulphides, quarried at the region of Valentia, S of Ireland. Stratigraphic level: Middle Devonian. Sample provided by the company Valentia Slate Ltd.

8 – Mica-schist from Finnmark, Norway. This is type of rock is not usually used for roofing. However, at N of Norway  are several quarries of different varieties of mica-schists thin enough to be used for roofing. These rocks have higher metamorphic degree and mineralogy clearly different to those of the slates s.s. Stratigraphic level: Lower Cambrian. Sample provided by Minera Skifer.

9 – Slate Valongo, Portugal. Dark slate, fine-textured, with some cubes of pyrite. It is quarried in the Valongo area, near Porto, in Portugal. It is similar to some levels of Galician slate, in Spain. Stratigraphic level: Middle Ordovician. Sample provided by Pereira Gomes & Carballo.

10 – Slate Green Lugo. This type of slate is extracted at the Pol area in the province of Lugo. It is characteristic its intense green color, result of the predominance of the magnesic term of the chlorite group, clinochlore. Stratigraphic level: Lower Cambrian. Sample provided by the company Pizarras Ipisa.

11 – Filita from Bernardos. Gray slate, coarse-textured, with no organic matter nor iron sulfides. It is extracted in Segovia, N of Madrid, and is the slate with which was built the Escorial Monastery roof. It has a slightly higher metamorphic degree compared with slates s.s., as evidenced by the presence of biotite. Stratigraphic level: Lower Cambrian. Sample provided by the company Pizarras J Bernardos.

12 – Ballachulish slate. This slate is from an historical quarry no longer in operation. It is a coarse-grained rock with abundant quartz grains and little or no iron sulfide. Sample collected in quarry.

And please remember: There are no bad slates but bad uses. The slate should be used in accordance with the building and environment requirements, so it is critical to know and understand the rock we are dealing with.

Roofing slates of the world, part I

Images of hand specimens and thin sections of slates from several world´s locations. Real color of the specimens may vary with respect of shown in the images.

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1 – Slate from Labassere, Pyrenees, France. Dark and homogeneous slate quarried in the French Pyrenees. Nowadays, the quarry keeps a small production focused in the local market. Stratigraphy: Ordovician. Sample picked directly at the quarry.

2 – Shale from Minas Gerais, Brazil. Green rock, although other colors are quarried. It has a metamorphic grade slightly lower than slate. Also, it may have carbonate inclusions (red colored zones in the 200 zoom microphotograph) located in sandy levels. Stratigraphy: Bambui group, Ediacaran. Sample courtesy of Pizarras SAMACA.

3 – Red slate from Newfoundland, Canada (Trinity slate). Fine-grained and homogeneous slate with abundant iron oxides which gives it the red color. Stratigraphy: Bonavista Formation, Lower Cambrian. Sample courtesy of Laboratorio del Centro Tecnológico de la Pizarra.

4 –Himalaya slate. This rock is actually a layered volcanic rock, as it can be deduced due to the epidote crystals seen in the thin section. There are some studies about roofing slates in the Nepal and Himalaya zone Himalaya (Neupane 2007, Neupane 2012). The production potential for this area is still unknown. Stratigraphy: Nourpul and Benighat Formations, Neoproterozoic/Lower Cambrian.

5 – Shale from Jiangxi, China. Light grey rock, fine grained, with homogeneous texture and abundant opaque minerals. Roofing slates form China are very varied both from  petrological and commercial points of view. Thus, there are some exceptional god materials together with other with less quality. Stratigraphy: Shuidonggou Formation, Silurian. Sample courtesy of StoneV.

6 – Angers slate, France. Dark and fine-grained slate, with homogeneous texture, very typical in France. It has been quarried for centuries. Startigraphy: Grand-Auverné Formation, Middle Ordovician. Sample courtesy of Ardosieres d´Angers.

And please remember: There are no bad slates but bad uses. The slate should be used in accordance with the building and environment requirements, so it is critical to know and understand the rock we are dealing with.

World´s roofing slate market in 2011

Producing countries versus consuming countries

A brief analysis of the global market for roofing slate in 2011 reveals a number of interesting conclusions. Spain still remains the largest exporter of slates in the world, followed by China and Brazil. Spanish exports in dollars (graphic 1) are well above those of China and Brazil, but not so for exports measured in tons (graphic 2), where China is close to the production volume of Spain. Regarding to consuming countries, in 2011 France was the largest consumer, followed by the UK, Germany and the United States.

Evolution 2011

Taking into account the selling prices for slate, measured in $/ton (graphic 3), Spain, the largest producer, sells its slate at an average price of $ 657/ton, down from the average of 855 $/ton. However, this price is higher than the sales of China (343 $/ton) and Brazil ($ 479/ton). In fact, the overall average price rises due to high sale prices of Central European countries (Germany, France, Belgium and Italy) that had a very limited production but sold at high prices their production into their own markets for restoration of historical monuments and singular buildings. On the other hand, the buying price (graphic 4) for all the countries is closer to the average (787 $/ton), except for the case of China (1,412 $/ton) and Brazil (1,071 $/ton). These two countries buy little roofing slate (graphics 1 and 2) but at very high prices. Thus, it is possible to draw a conclusion: China, and to a lesser extent Brazil, are potential consumers of roofing slate. The opening of these markets to European production companies can be a good solution for the economic crisis that many of these companies are experiencing.

Statistical data: http://comtrade.un.org, code 6803, category HS2002

Roofing slate deposits in the world

There are several roofing slate deposits in the world. The biggest is located in the northwest of the Iberian Peninsula, although there are other large reserves which are not yet evaluated in China and Brazil. Thus, the main producers of roofing slate are Spain, China and Brazil, in that order.

Evolution of the roofing slate trade. Data: UNSTASTS, http://comtrade.un.org

Evolution of the roofing slate trade. Data: UNSTASTS, http://comtrade.un.org

The sector has been hardly hit by the global crisis of recent years, but the production is beginning to recover in Spain, although China is gaining ground especially in volume of production. However, Chinese slate is sold at a price significantly lower than the Spanish, hindering the takeoff of a strong slate production sector in this country. First consumers of Spanish slate are France, Germany and the UK:Grafico Imp paises_ENG

From a petrological point of view, the commercial denomination “roofing slate” includes various types of rocks, with the common characteristic that can exfoliate in large and thin tiles. The specific characteristic of each type of slate depends on its petrology. These specific characteristics control the performance of a slate depending on the conditions of use and the climate.

World´s main deposits of roofing slates.

World´s main deposits of roofing slates.