Slates are an essential building material used at a large scale in the construction of buildings. Their solid beauty achieves a visual harmony with the stone buildings and the drystone walls. Slate stones are also known as grey slates, flags, flagstones, thackstones, slats, flatstones, stone tiles and tilestones.
Slate is chiefly comprised of quartz and illite, with mica, calcite, and minor quantities of other various minerals. Slates vary in color, most commonly seen in black, gray, red, purple, or green. The red color is due to the presence of Hematite, while green colors are due to Chlorite. Grey and black are due to carbon and/or graphite. Shades of red, purple and tan are related to varying amounts of iron oxides.