sedimentary

Glauconitic Sandstone (Greenstone)

Glauconitic Siliciclastic Sandstone (K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2

Hardness: 2-3 (glauconite) to 7 (quartz matrix), Color: Dull olive green to blue-green, Luster: Earthy to dull, Crystal Structure: Monoclinic (micaceous), Cleavage: Perfect basal (rarely visible in hand specimen), Specific Gravity: 2.4-2.9

Identified March 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine continental shelf environments through the slow accumulation of detrital sediments and the biochemical alteration of organic debris or mica. Common in the Cretaceous and Tertiary periods, typically in low-oxygen marine settings.

Uses & applications

Used historically as a source of potassium for soil fertilizer (greensand). In some regions, it is used as a water softener due to its ion-exchange properties. Smaller, polished pieces are occasionally used in folk jewelry or as garden decorative stones.

Geological facts

The presence of glauconite indicates a very slow rate of sedimentation. It is often referred to as 'Greensand' and was once a primary source of potash in the United States, particularly in New Jersey and the Gulf Coast.

Field identification & locations

Identify by its characteristic dull green color and granular, sandy texture. It often feels slightly gritty and may leave a light green streak if soft. Commonly found in coastal plains, riverbanks of ancient seabeds, and eroded sedimentary outcrops.

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