1.
n. [Geology]
[(K,Na,Ca) 1.2-2.0(Fe+3,Al,Fe+2,Mg)4(Si7-7.6Al1-0.4O20)(OH)47nH20]
A green
silicate mineral found in
sedimentary rocks and formed on continental shelves characterized by slow
sedimentation and organic matter, such as fecal pellets, present in an oxidizing environment. In sufficient quantity, it can form a sandy, green
deposit such as the Cretaceous greensands of the US and UK.