(Labib and Eden, 2005)

Slate is a fine-grained metamorphic rock with a flat plate-like structure that gives the rock its ability to be easily split into thin sheets for roofing.

In the UK, slate is quarried in Wales (Welsh Slate), Cumbria (Burlington Slate) and Cornwall (Delabole). The largest resources are in North Wales, where the Penrhyn Quarry was at the end of the 19th century the largest slate quarry in the world.

The extraction and working of slate results in an extremely high proportion of waste rock in the form of aggregate and fines. Estimates vary between 9 and 20 tonnes of waste generated for every 1 tonne of saleable slate product (Goulden, 1992; Mitchell, 2016).

Coarse slate waste can be utilised as a construction aggregate, but the distance of the slate stockpiles from the main urban aggregate markets has limited the extent to which the waste is used, meaning that each year stockpiles of slate waste still increase . There are over 700 million tonnes of waste accumulated in Gwynedd, North Wales (Welsh Assembly Government, 2004).