sedimentary
Glauconitic Sandstone with possible Trace Fossil
Glauconitic Sandstone (K(Fe,Al)2(Si,Al)4O10(OH)2)
Hardness: 2-3 (glauconite) to 7 (quartz matrix); Color: Dull green to dark green grains in a tan/grey matrix; Luster: Earthy to dull; Crystal structure: Monoclinic (micaceous); Specific Gravity: 2.4-2.9
- Hardness
- 2-3 (glauconite) to 7 (quartz matrix)
- Color
- Dull green to dark green grains in a tan/grey matrix
- Luster
- Earthy to dull
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Physical properties
Hardness: 2-3 (glauconite) to 7 (quartz matrix); Color: Dull green to dark green grains in a tan/grey matrix; Luster: Earthy to dull; Crystal structure: Monoclinic (micaceous); Specific Gravity: 2.4-2.9
Formation & geological history
Formed in marine shelf environments with slow sedimentation rates, typically under reducing conditions. This specimen appears to contain a dark green concentration of glauconite mineral within a clastic sandstone matrix, possibly infilling a burrow or trace fossil.
Uses & applications
Glauconite is used as a soil conditioner and fertilizer (greensand), in water softening, and historically as a pigment. The host sandstone is used in general construction.
Geological facts
Glauconite is often referred to as 'greensand'. Because it forms only in marine environments, its presence is a diagnostic indicator of ancient sea beds. The dark green heart-like shape in the specimen is likely a cross-section of a fossilized burrow.
Field identification & locations
Identify by its characteristic dull 'olive' green color and sandy texture. It is commonly found in Cretaceous and Paleogene sedimentary sequences globally, particularly in coastal plains like the eastern USA or southern UK.
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