sedimentary
Glauconitic Sandstone
Glauconitic Sandstone (complex silicate formula: (K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2)
Hardness: 2-3 (for individual grains), 6-7 (if silicified matrix); Color: dull green to grayish-green; Luster: earthy to dull; Crystal structure: monoclinic (micaceous); Specific Gravity: 2.4 - 2.85.
- Hardness
- 2-3 (for individual grains), 6-7 (if silicified matrix)
- Color
- dull green to grayish-green
- Luster
- earthy to dull
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Physical properties
Hardness: 2-3 (for individual grains), 6-7 (if silicified matrix); Color: dull green to grayish-green; Luster: earthy to dull; Crystal structure: monoclinic (micaceous); Specific Gravity: 2.4 - 2.85.
Formation & geological history
Formed in marine shelf environments with slow rates of accumulation, typically during high sea-level stands. It is an authigenic mineral that forms via the modification of fecal pellets or debris of other minerals in reducing environments.
Uses & applications
Used historically as a green pigment ('green earth') in painting, as a water softener due to its ion-exchange properties, and in agriculture as a slow-release potassium fertilizer (greensand).
Geological facts
The presence of glauconite is often used by geologists as an indicator of a marine depositional environment and a slow rate of sedimentation. It is frequently associated with offshore continental shelf deposits.
Field identification & locations
Identify in the field by its distinct dull olive-green color and 'sandy' feel. It is often found in Cretaceous or Tertiary marine strata. Collectors should look for 'greensand' beds in coastal regions like the New Jersey coastal plain or parts of the UK.
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