glauconite

Scope note: A dull green mica mineral composed of hydrated potassium iron silicate, that -- unlike other micas -- usually occurs as pelletlike grains in marine environments and is sometimes called "green sand." It is formed from the alteration of iron-bearing silicates by ocean water and organisms, is found along the Atlantic coast of the North and South America and on the ocean floors, and is sometimes used as a green earth pigment for paints.

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