Slate

[Eternit roofing.](By Harald Weber, CC BY-SA 3.0, Link)
Interesting origin of slate. First, to cover the roof people used clay shale, which consisted of small grains of clay minerals, which are oriented strictly parallel. In addition, the shiver was also used as a grinding material. In that case, he had to contain silicon. As we know silicon oxide on an equal basis with corundum in the modern world is used as an abrasive for the isotization of all kinds of materials.
Over time, people began to make slate. Shaver production was based on the use of asbestos and cement. When people realized that asbestos is dangerous, it was replaced with fibers of cellulose and mineral fillers. That's the way the slate passed from stone to product.