sedimentary
Glauconite (Greensand)
Glauconite (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2
Dull earthy luster, green to dark green color, soft (Hardness 2 on Mohs scale), friable or crumbly texture, monoclinic crystal structure in microscopic scales.
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Physical properties
Dull earthy luster, green to dark green color, soft (Hardness 2 on Mohs scale), friable or crumbly texture, monoclinic crystal structure in microscopic scales.
Formation & geological history
Formed in marine environments through the alteration of minerals like mica or fecal pellets in shallow, oxygen-poor waters. High concentrations define geologic formations called greensands, typically dating from the Cretaceous or Tertiary periods.
Uses & applications
Primarily used as a slow-release natural fertilizer and soil conditioner due to its potassium and iron content. Historically used as a green pigment and in water-softening applications.
Geological facts
Glauconite is an indicator mineral for marine depositional environments and is often used by geologists to date sedimentary layers through potassium-argon dating.
Field identification & locations
Identify by its distinctive olive-green color and tendency to crumble into sand-like grains when rubbed. Commonly found in coastal plains like those in New Jersey, Delaware, and parts of the United Kingdom.
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