The ”Roofing slates of the world” map
13 juli 2022
This map is the result of more than 15 years of research. It depicts past and present roofing slate outcrops of the world, and it is continuously being updated. Main outcrops are represented by the actual image of the slates, obtained from actual samples using an optical scanner. Active quarries are represented by a square, while exhausted or non-working sites have the form of an octagon. Besides, each outcrop present information about country and region, together with the code according the International Classification of Roofing Slates (IRSC). The IRSC classifies roofing slates into 12 categories according to their type of rock and colour.
There are four rocks used as roofing slates:
Code 0, metalutite or low grade slate, such as the slates from Brazil
Code 1, real and orthodox slate, which corresponds to most of the roofing slates traded in the world. Good examples are the Spanish slates from Valdeorras, Welsh slates, or the exhausted slates from Germany and France.
Code 2, phyllites, a scarce and crystalline type of roofing slate only available from Bernardos (Spain), San Luis (Argentina), and some areas of Scandinavia.
Code 3, mica schist, also scarce and hard, mainly found on Scandinavia
On the other hand, colour is the result of the mineralogical content of the roofing slate. There are three colour families:
Black (B), the commonest colour, given by small amounts of organic components such as coal.
Green (G), due to the occurrence of a green mineral named clinochlore.
And Purple-Red (R), result of a small amount of iron oxide. These slates do not have pyrite or other oxidizing minerals, since all oxide is already created.
The combination of these features results in the IRSC 12 categories of roofing slates. More information on how the meaning of these features and their application to the roofing slate market can be found on the scientific paper Cárdenes V, Rubio-Ordoñez A, Ruiz de Argandoña VG. Definition of Roofing Slate Lithotypes for an International Roofing Slate Classification. Key Materials in Engineering. 2020;848:48-57.