Buff Sandstone, Coursed Ashlar

A fine to medium grained, light buff coloured sandstone. Sandstone is a sedimentary rock composed largely of quartz, with a high silica and calcium carbonate content that has been widely used in architecture for millennia for its gorgeous, reassuring, warm colours and soft, uniform surface appearance yet robust, durable and mechanically strong characteristics. Excellent historic examples of sandstone include the ancient temple and caves of Petra, Jordan, and the Red Fort in Delhi, India, to the stunning rhythm and uniformity of tenement blocks of flats in Edinburgh and Glasgow, Scotland. It is also crushed and used for hardcore or aggregate in construction projects, though its use is less common due to the porosity between its sand particles and the binding agent. Sandstone forms when granules are weathered away from other types of rock and are subject to a sequence of weathering and erosion known as denudation. Mechanical weathering from ice, water flow, waves, rain, wind or thermal activity strips or grinds down parts of the origin rock, with particles being transported, or eroded, away from the source area by glaciers, rivers, wind or water, with high concentrations of the particles being deposited in one area. In sandstone’s case, this is typically in bodies of water. The transportation process helps destroy granules of weaker minerals, while rounding and smooth the stronger minerals, typically quartz. The higher the quartz content of sandstone, the more mature and robust it is considered. The particles then undergo a process known as lithification over an extensive period of time, whereby particles are compacted in layers, compressed under their own weight and bound or cemented together when exposed to and combined with chemicals such as silica and calcium carbonate or, in the case of red sandstone, higher concentrations of iron oxide, which help increase the bond between the granules and reduce the porosity of the newly formed rock. The process of denudation, erosion and formation of the new rock is known as sedimentation.