sedimentary
Glauconitic Sandstone (Greensand)
Glauconitic Quartz Arenite (containing Glauconite, (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2)
Hardness: 2-3 (Mohs for glauconite), variable for sandstone; Color: Dull olive-green to dark blackish-green; Luster: Dull or earthy; Crystal Structure: Monoclinic (microcrystalline); Cleavage: Perfect mica-like cleavage (rarely visible in hand specimen); Specific Gravity: 2.4-2.9.
- Hardness
- 2-3 (Mohs for glauconite), variable for sandstone
- Color
- Dull olive-green to dark blackish-green
- Luster
- Dull or earthy
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Physical properties
Hardness: 2-3 (Mohs for glauconite), variable for sandstone; Color: Dull olive-green to dark blackish-green; Luster: Dull or earthy; Crystal Structure: Monoclinic (microcrystalline); Cleavage: Perfect mica-like cleavage (rarely visible in hand specimen); Specific Gravity: 2.4-2.9.
Formation & geological history
Formed in marine environments through the slow biochemical alteration of organic matter or fecal pellets in shallow shelves. Typically dates from the Cambrian to the Cenozoic eras, often found in 'greensand' stratigraphic layers.
Uses & applications
Used historically as a slow-release potassium and iron fertilizer in organic farming. Also used in water softening due to its ion-exchange properties and occasionally as a low-quality building stone or road fill.
Geological facts
Glauconite is considered an 'indicator mineral' for marine depositional environments; its presence almost always proves the rock was formed in seawater. It is also a member of the mica group of minerals.
Field identification & locations
Identify by its characteristic dull green color and crumbly (friable) texture. It often feels gritty due to quartz content and may stain fingers green when handled. Common in coastal regions like the Atlantic Plain (USA), United Kingdom, and Australia.
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