sedimentary
Glauconite
Glauconite (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2
Hardness: 2.0; Color: Olive green, dark green, or blue-green; Luster: Dull to pearly; Crystal Structure: Monoclinic; Cleavage: Perfect basal; Specific Gravity: 2.4-2.95.
- Hardness
- 2
- Color
- Olive green, dark green, or blue-green
- Luster
- Dull to pearly
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Physical properties
Hardness: 2.0; Color: Olive green, dark green, or blue-green; Luster: Dull to pearly; Crystal Structure: Monoclinic; Cleavage: Perfect basal; Specific Gravity: 2.4-2.95.
Formation & geological history
Forms in marine environments, specifically on continental shelves with slow sedimentation rates. It is an authigenic mineral, typically forming from the alteration of mica or fecal pellets in shallow seas. Most common in Cretaceous and Cenozoic sediments.
Uses & applications
Mainly used as a soil conditioner (green sand) in agriculture due to its potassium content. It was historically used as a pigment for green oil paints and sometimes in water softening systems.
Geological facts
The presence of glauconite is a key indicator for geologists of a marine depositional environment and a period of 'starved' sedimentation, where very little new sediment was being added to the seafloor.
Field identification & locations
Identify by its distinctive dark green color and earthy texture in sedimentary sandstones or limestones. It is often found as small, rounded pellets (greensand) in coastal regions like New Jersey, USA, and various sites in Europe.
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