sedimentary
Glauconite (Greensand)
Glauconite ((K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2)
Hardness: 2 Mohs; Color: dull green to bluish-green; Luster: dull to earthy; Structure: monoclinic (often found as small rounded pellets); Cleavage: perfect (rarely seen in grains)
- Hardness
- 2 Mohs
- Color
- dull green to bluish-green
- Luster
- dull to earthy
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Physical properties
Hardness: 2 Mohs; Color: dull green to bluish-green; Luster: dull to earthy; Structure: monoclinic (often found as small rounded pellets); Cleavage: perfect (rarely seen in grains)
Formation & geological history
Formed in marine environments through slow sedimentation in shallow waters; typically associated with continental shelf deposits and dates from the Cambrian to the present.
Uses & applications
Used as a soil conditioner and slow-release potassium fertilizer; historically used as a green pigment and for water softening via ion exchange.
Geological facts
Glauconite is an 'authentigenic' mineral, meaning it forms in place on the seafloor. Its presence in a rock formation is a strong indicator of a slow rate of sedimentation in a marine environment.
Field identification & locations
Identify by its distinctive earthy green color and tendency to crumble into smaller grains. Commonly found in 'Greensand' formations in New Jersey, USA, and along the English coast.
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