It was formed in the Upper Miocene (12-7.5 Million years ago). This is a very thin rock layer which is found only in particular locations such as il-Gelmus in Gozo where it is found at its maximum thickness of 12m. In other areas it is just 1m thick. The name implies that it is green in colour however when it is exposed it turns into a distinctive orange colour.
Below: Gelmus Hill, where Greensand is exposed at its maximum thickness just below the surface of the plateau. The sides of the hill are a clay talus.