sedimentary
Glauconitic Sandstone
Glauconitic Quartz Sandstone (K(Fe,Al)2(Si,Al)4O10(OH)2)
Hardness: 6-7 (quartz matrix), 2 (glauconite grains); Color: Dark green to brown-green patches; Luster: Dull to earthy; Crystal structure: Monoclinic (glauconite), Hexagonal (quartz); Specific gravity: 2.4-2.9
- Hardness
- 6-7 (quartz matrix), 2 (glauconite grains)
- Color
- Dark green to brown-green patches
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (quartz matrix), 2 (glauconite grains); Color: Dark green to brown-green patches; Luster: Dull to earthy; Crystal structure: Monoclinic (glauconite), Hexagonal (quartz); Specific gravity: 2.4-2.9
Formation & geological history
Formed in marine environments through the alteration of minerals or organic matter on the seafloor during periods of slow sedimentation. Commonly dated to the Cretaceous or Cenozoic periods.
Uses & applications
Used primarily as a soil conditioner (greensand) due to potassium content, or as a filter medium in water treatment. Historically used as a green pigment.
Geological facts
Glauconite is often referred to as 'greensand' and is a key indicator for geologists that a specific rock layer was formed in a shallow marine environment.
Field identification & locations
Identify by its distinctive dark green or olive-green specks within a sandy matrix. Common in coastal plain regions like New Jersey, USA, or coastal England. It feels gritty and the green spots can sometimes be rubbed off as a powder.
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