Malmstone

Greensand or Green sand is either a sand or sandstone, which has a greenish color. This term is specifically applied to shallow marine sediment, that contains noticeable quantities of rounded greenish grains. These grains are called glauconies and consist of a mixture of mixed-layer clay minerals, such as smectite and glauconite mica. Greensand is also loosely applied to any glauconitic sediment.

Greensand forms in anoxic marine environments that are rich in organic detritus and low in sedimentary input. Having accumulated in marine environments, greensands can be fossil-rich, such as in the late-Cretaceous deposits of New Jersey, USA.

Important exposures are known from both northern and western Europe, North America, and north Africa. Well known and important greensands are the Upper and Lower Greensands of England and occur within Eocene and Cretaceous sedimentary strata underlying the coastal plains of New Jersey and Delaware. Although greensand has been found throughout Phanerozoic and Late Precambrian sedimentary deposits, it appears to be most common in Eocene, Cambrian, and Cretaceous sedimentary deposits for unknown reasons.

In Great Britain, greensand usually refers to specific rock strata of Early Cretaceous age. A distinction is made between the Upper Greensand and Lower Greensand. The term greensand was originally applied by William Smith to glauconitic sandstones in the west of England and subsequently used for the similar deposits of the Weald, before it was appreciated that the latter are actually two distinct formations separated by the Gault Clay. The Upper Greensand was also once known as either the "Malm" or "Malm Rock Of Western Sussex"

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