sedimentary
Glauconite (Greensand)
Glauconite (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2
Hardness: 2 Mohs; Color: Dull green, olive green, or blue-green; Luster: Dull to earthy; Crystal Structure: Monoclinic; Cleavage: Perfect mica-like; Specific Gravity: 2.4-2.95
- Hardness
- 2 Mohs
- Color
- Dull green, olive green, or blue-green
- Luster
- Dull to earthy
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Physical properties
Hardness: 2 Mohs; Color: Dull green, olive green, or blue-green; Luster: Dull to earthy; Crystal Structure: Monoclinic; Cleavage: Perfect mica-like; Specific Gravity: 2.4-2.95
Formation & geological history
Formed in marine environments on the continental shelf through slow accumulation and shallow-water chemical alteration of fecal pellets and organic matter. Typically found in Cretaceous and Tertiary marine sediments.
Uses & applications
Used as an organic fertilizer (greensand) for potassium, a water softener (ion exchange), and historically as a green pigment in paints.
Geological facts
Glauconite is an 'atypical' mica that grows directly in salt water and is a key indicator of shallow marine depositional environments in the geological record.
Field identification & locations
Identified by its distinctive dull green color and crumbly texture. Often found in sandy formations ('greensands') along coastal regions like the US Eastern Seaboard, particularly New Jersey and Delaware.
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