sedimentary

Glauconitic Sandstone (Greensand)

Glauconitic Quartz Arenite (Formula: (K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2)

Hardness: 6.5-7 (sandstone matrix), 2 (glauconite grains); Color: Dull green, olive, or bluish-gray; Luster: Dull to earthy; Crystal structure: Monoclinic (microscopic glauconite within granular matrix); Specific gravity: 2.4-2.8

Hardness: 6
Color: Dull green, olive, or bluish-gray
Luster: Dull to earthy

Identified February 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments on continental shelves through the slow deposition of sand mixed with authigenic glauconite. It typically dates from the Cretaceous or Tertiary periods and indicates low oxygen levels during formation.

Uses & applications

Used primarily as a soil conditioner and natural fertilizer due to potassium content. It is also used in water filtration systems for mineral removal and occasionally as a low-grade decorative building stone.

Geological facts

Also known as 'Green Earth,' the glauconite within this rock has been used as a pigment in green oil paints since Roman times. It is considered a 'slow-release' fertilizer, often taking years to fully break down in soil.

Field identification & locations

Identify in the field by its distinctive green hue and crumbly (friable) texture; it often leaves a green stain on the fingers when rubbed vigorously. Common in coastal regions like New Jersey (USA) and the south of England.

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