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.

Pizarras del Mundo02

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.