Caithness flagstone has unique qualities that distinguish it fundamentally from most natural rock formations. It is a sedimentary rock that was formed when mud settled at the bottom of an ancient lake and became compressed over time. There are distinct horizontal layers of this hard sediment that are readily split open to reveal flat surfaces that can be very smooth and of diverse and beautiful textures, undisturbed since the time they were formed. This is the most notable feature of Caithness flagstone. Most other stones are split and worked by tools and the surface you see, whether rough or smooth, is the product of that working.
The flat flagstone beds are broken up by vertical seams also. In different locations, the beds may be very large with few vertical breaks, or smaller with frequent cracks. The large beds render the best flagstone pieces. However, the vertical seams are the secondary attractive feature of this stone; we call them natural edges. Quarries that have lots of vertical seams produce smaller stones which are excellent for building walls and dykes. They are used to great effect in the county of Caithness.
Stones of various sizes can also be used in many outdoor applications, taking advantage of both the horizontal riven surface and the natural external edges where these are also visible, for example as steps, small stepping stones, large plinths, outdoor benches and tables, waterfalls or pond edging.