Slate is a versatile and durable stone. It is formed under the earth surface, due to the influence of pressure and high temperatures on fine-grained rocks of silt and clay, which form slate clay. The structure of this rock also contains mica enough to form smooth and shiny texture. Slate is formed as blocks or slabs, but since it contains mica, slate easily splits into plates, so it is very easy to produce slate facing tiles or special “plate-scales,” used for making famous slate roofs. Note that the discovery of slate as a cladding material was owned by «Italardesia» in 1804. But the peculiarities of this mineral have been studied by family of miners from Val Fontanabuona (the Province of Genoa) for several generations.
Slate and its peculiarities
Slate is characterized by durability, strength and excellent wear resistance. It is also waterproof material, the coefficient of water absorption is only 0.01 – 0.3%. Slate is absolutely refractory. It is also resistant to any external effects, including chemicals. Slate is plastic material, due to what the products with a very complex geometry are made of it. Plus, it does not crack or deform for many hundreds of years. Traditionally, the color range of slate comprises the whole palette of dark and gloomy shades, but there are also gray-green, brown, yellow and purple hues. Note that there is also green slate (due to certain minerals in the structure) with graphite and brownish-red hues. Once used, for example, for exterior finishing, slate does not tarnish.
Traditionally, there are two groups of slate – crystalline slate and shale.
Slate with a crystal structure has dark colors, and comprises mainly feldspars. Such slate is used as a building material, as well as a refractory raw material.
Shale is represented by several types. Grapholite is softer and has a distinctive gray hue. The split forms long columns. Turkey-stone is very hard, it has a yellow-gray or greenish-gray tint. Carbonaceous shale (German “der Zeichenschiefer”, French “schiste-crayon”) is soft and contains high-carbonaceous matter of black color.
Slate and its use
The use of slate is known since Ancient Rome. The laying of slate flooring became fashionable exactly in Italy. It is a very strong and durable material, so it can be used not only for interior decoration but also for exterior cladding. The interior of slate is well combined with wood, metal (in particular, with the artistic forging), ceramics, glass, and other natural stones. In addition to facing tiles for walls and floor (including bathrooms), countertops and tile for fireplace finishing are also made of slate. By the way, slate finishing of fireplaces is the tradition that came from Liguria. In particular, there was a special recipe for roasting meat on the hot shale, which was put on top of the coals. It may be said to be the prototype of the modern grill. Slate looks no less impressive as inlays in different furniture. Another interesting use of the slate was first presented in England in 1826. John Tuston showed this material to coat the surface of a billiard table. Note that today this trend remains unchanged. The best for this are Italian slate and Brazilian slate (but it is less flexible, than Italian). Shale brick is also used in construction. It is suitable for the construction of socle, walls, different partitions and other architectural elements. Slate is exclusively elite material for paving and covering of different areas. Nevertheless, it is widely used in landscape design: as lining for rock gardens, artificial ponds, retaining walls for raised flowerbeds and terraces, artificial grottoes and rocks. Finally, we note the use of slate as a roofing material. The first peculiarity is high cost of this material. The second peculiarity is delight with this material, which has no analogues, remains out of fashion trends and time. Plastic, miniature slate plate-scales of any size and shape make it possible to translate into reality the most unusual and complex roofs with any geometry and design. Just as well-known roof tile, these plates may be zigzag, wavy, and of any other format. But none of the other materials is similar and comparable to this roofing. Despite the fact that Genoa is called “slate museum in the open air”, and the slate roofs of Buckingham Palace and the Louvre, as well as many other architectural masterpieces of England and Germany, for so many centuries were shining perfectly as if they have just been cleaned out, the slate as a roofing material is called unique even today. Let’s just say fashion changes, style changes, states change, but the slate remains.