sedimentary
Glauconitic Sandstone
Glauconitic Quartz-Wacke / Sandstone (Fe(II),Fe(III),Al,Mg)2-3(Si,Al)4O10(OH)2
Hardness: 2-3 (for the glauconite grains) to 7 (for the quartz matrix); Color: Dull olive green to earthy grayish-green; Luster: Earthy, dull; Crystal structure: Monoclinic (microcrystalline grains); Specific Gravity: 2.4 - 2.9
- Hardness
- 2-3 (for the glauconite grains) to 7 (for the quartz matrix)
- Color
- Dull olive green to earthy grayish-green
- Luster
- Earthy, dull
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Physical properties
Hardness: 2-3 (for the glauconite grains) to 7 (for the quartz matrix); Color: Dull olive green to earthy grayish-green; Luster: Earthy, dull; Crystal structure: Monoclinic (microcrystalline grains); Specific Gravity: 2.4 - 2.9
Formation & geological history
Formed in marine environments on continental shelves with slow sedimentation rates. Glauconite forms authigenically through the alteration of detrital minerals (like biotite) or fecal pellets in reducing seafloor conditions. These rocks often date from the Cretaceous to the Cenozoic eras.
Uses & applications
Used primarily as a soil conditioner and source of potassium (greensand) in organic farming. Also used historically as a green pigment and occasionally as a water softener due to its ion-exchange properties.
Geological facts
Glauconite is often referred to as 'Greensand.' It is an indicator of marine depositional environments and is frequently used by geologists to date sedimentary sequences through potassium-argon dating.
Field identification & locations
Identify in the field by its distinct dull green color and sandy texture; it often leaves a green streak if crushed. Commonly found in coastal plains, such as the Atlantic Coastal Plain of the USA and parts of the UK and Belgium.
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