Glauconite (Greensand)
Glauconite (Dioctahedral Mica Group) · Mineral Specimen / Industrial Mineral / Sedimentary Rock Component
Crystal System
Monoclinic; typically occurs as microcrystalline, earthy, or pelletal aggregates (massive/granular habit).
Mineral Group
Silicates (Phyllosilicate subgroup, Mica group)
Chemical Formula
(K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2
Formation Process
Sedimentary (Authigenic); forms through the slow chemical alteration of organic fecal pellets or mineral grains in shallow marine environments under reducing conditions.
About This Crystal
An opaque, dull to earthy green mineral often appearing as granular aggregates. It exhibits a dark olive-green to blue-green color with yellowish-brown oxidation crusts.
Physical Characteristics
Color: Olive green to blackish-green; Streak: Green to light grey; Fracture: Uneven; Specific Gravity: 2.4 - 2.95; Luster: Dull to earthy.
Optical Properties
Sub-translucent to opaque; Refractive index: 1.590 - 1.645; Non-fluorescent; Birefringence is high but usually masked by the mineral's fine-grained nature.
Hardness & Durability
Origin Region
Common in marine sedimentary basins worldwide; notable deposits in New Jersey (USA), Kent (UK), and Normandy (France).
Hardness & Durability
Mohs Hardness: 2.0; very soft and brittle; poor wearability for jewelry; easily crushed into powder.
Care & Maintenance
Extremely fragile. Avoid water (may cause crumbling), ultrasonic cleaners, and chemicals. Store in a dry, stable environment away from harder minerals.
Rarity & Value
Very common globally; low monetary value for individual specimens. Primarily valued as a soil amendment (fertilizer) or for geological dating (K-Ar dating).
Special Characteristics
Known for its green color in 'greensand' deposits; often contains microscopic fossils or serves as a replacement mineral for organic matter.
Lore & History
Used historically as a green pigment (Terre Verte) in European Renaissance painting and traditionally used by coastal cultures as a natural potassium-rich fertilizer.