What Is Greensand?

Greensand is a type of rock formed from volcanic ash or lava. It consists mainly of calcium carbonate (CaCO3) with trace amounts of other minerals such as silica, magnesium oxide, iron oxides and potassium nitrate. These are all common elements found in nature but they have been chemically altered so that they can be used as building blocks for concrete, mortar and bricks.

The term “greensand” was first used in 1847 by a British chemist called William Greenstone. His name is now synonymous with the word “green”. However, it wasn’t until the late 19th century that the term began being applied to natural rocks like limestone and dolomite which were not considered valuable enough to be mined commercially.

Thus, when someone suggested using them as building material, they became known as “greensands.”

How Does It Work?

Green sand is made up of tiny particles of clay, silt and fine gravel. When these small particles come into contact with water, they form a gel. This gel hardens quickly under pressure making it ideal for use as a building material. If you break the surface tension between the liquid and solid phases, then you create a weak point in the cementitious matrix that holds together your wall. The more solid you make the weak point, the stronger your wall.

By varying the mixture of sand, clay or shale and water, you can create a mortar that hardens in different strengths. This is why the strength of greensand is measured by its drying time. Green sand should be used quickly as it begins to dry out after 48 hours during which time it can change its consistency and compromise its quality.

Sources & references used in this article:

The stratigraphy of the Upper Greensand (Cretaceous) of south-west England by GR Mansfield – 1922 – US Government Printing Office

Comparison of minor elements in the Upper Greensand and Thanet Beds of Southeast England by R Gallois – Geoscience in south-west England: proceedings of the …, 2005 – nora.nerc.ac.uk

The sedimentology, petrology and stratigraphy of the Upper Greensand in SW England by HH Le Riche – Geoderma, 1977 – Elsevier

Attenuation of potential pollutants in landfill leachate by Lower Greensand by CL Williams – 1991 – pearl.plymouth.ac.uk

Economic potential of glauconitic rocks in Bakchar deposit (SE Western Siberia) for alternate potash fertilizer by DJV Campbell, A Parker, JF Rees, CAM Ross – Waste Management & …, 1983 – Elsevier

Groundwater recharge in the Lower Greensand of the London Basin—results of tritium and carbon-14 determinations by M Rudmin, S Banerjee, A Mazurov, B Makarov… – Applied Clay …, 2017 – Elsevier

The stratigraphy and petrography of the Gault Clay Formation (Albian, Cretaceous) at Redcliff, Isle of Wight by JD Mather, DA Gray, RA Allen… – Quarterly Journal of …, 1973 – qjegh.lyellcollection.org

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