Red limestones usually contain haematite; in green limestones there may be glauconite or chlorite.
The green sand when weathered is brown or rusty coloured, the glauconite being oxidized to limonite.
Dark “green-sands,” very rich in glauconite, are followed by yellow sandstones with some flint.
Grains of glauconite can easily be seen in a handful of sand,—better with a magnifying glass.
Calcareous sands or impure limestones with glauconite are also by no means rare, an example being the well-known Kentish Rag.
The sandstones are grey in colour, weathering buff or reddish-brown, tinged more or less green by grains of glauconite.
The colouring matter is believed in every case to be glauconite.
They may be seen occupying these shells, and when the shell is dissolved away perfect casts of glauconite are set free.