Slate (writing) expensive. Slate (writing) A slate is a thin piece of hard flat material, such as the rock also called slate, that is used as a medium for writing. The rock is “a metamorphic rock created by the recrystallization of the minerals in shale from clay to parallel-aligned, flat, flake-like minerals such as mica”. The writing slate consisted of a piece of slate, typically either 4x6 inches or 7x10 inches, encased in a wooden frame. A precise date range for writing slates of this type has not been established. Usually, a piece of cloth or slate sponge was used to clean
Aberllefenni Slate Quarry slates. Foel Grochan mine consists of eight near-horizontal tunnels at approximately vertical separation. These were bored into the valley side just to the north of the near-vertical narrow vein. Each tunnel connected to a large chamber from which the rock was extracted. These chambers ranged from to in length with of rock left between the bottom of one chamber and the top of the next lower chamber. As more slate was extracted, several of the upper chambers were joined vertically to form an extremely large cavern known as Twll Golau which is open at the top. From the mid-1850s the