Glauconitic Sandstone
“Green-speckled sand from the continental shelf”
Glauconitic sandstone is a quartz sandstone containing the distinctive green mineral glauconite, which forms authigenically (in place) on the sea floor under low-oxygen conditions. The green glauconite grains scattered through lighter quartz sand give the rock a characteristic speckled appearance.
quartz, glauconite, feldspar, clay minerals, calcite cement, phosphate (minor)
New Jersey Coastal Plain (USA), Lower Greensand (England), Paris Basin (France), Australian shelf deposits, Cretaceous formations worldwide
4-6
Glauconite is useful for radiometric dating using the potassium-argon method because it contains potassium — allowing geologists to directly date the age of the sediment it formed in, rather than relying on fossils alone.
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