Slate tiles HEAVY 3, 40×25

Heavy shale 3 is produced from the CUPA PIZARRAS No 3 quarry in San Pedro de Trones (León) in northern Spain.

The shade is bluish black with a slightly granular texture, some samples showing parallel lines on the cleavage surfaces.

Another obvious feature of this shale is the presence of metal grains measuring about 2 mm. Sometimes they are randomly distributed throughout the sheet, while in other cases they are concentrated in individual bearing layers. They are iron sulphide, known as pyrites. The 7mm thickness and weight give it the ability to withstand high wind speeds and heavy rainfall.