sedimentary
Glauconitic Sandstone
Glauconite (K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2 in Quartz Sandstone
Hardness: 2-3 for glauconite, 7 for quartz grains; Color: Dull green to dark green grains in a tan or grey matrix; Luster: Earthy to dull; Crystal structure: Monoclinic (micaceous); Specific Gravity: 2.4-2.9.
- Hardness
- 2-3 for glauconite, 7 for quartz grains
- Color
- Dull green to dark green grains in a tan or grey matrix
- Luster
- Earthy to dull
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Physical properties
Hardness: 2-3 for glauconite, 7 for quartz grains; Color: Dull green to dark green grains in a tan or grey matrix; Luster: Earthy to dull; Crystal structure: Monoclinic (micaceous); Specific Gravity: 2.4-2.9.
Formation & geological history
Formed in marine environments as a result of chemical alteration of organic matter or iron-rich minerals on the seafloor. Typically found in inner-shelf shallow marine deposits from the Paleozoic to the Cenozoic era.
Uses & applications
Used historically as a green pigment and as a slow-release potassium fertilizer in agriculture (greensand). It is also used as a water softener due to its ion-exchange properties.
Geological facts
Glauconite is an 'interstitial' mineral that often fills the cavities of small fossils or fecal pellets. Its presence is a strong indicator of a slow rate of sediment accumulation in a marine setting.
Field identification & locations
Identify in the field by looking for distinct green, rounded grains (pellets) within a sandy or silty matrix. It is commonly found in coastal plain regions like New Jersey (USA) or the Isle of Wight (UK).
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