Marl Concretions (Marlekor)
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Mineral NameMarl Concretions (Marlekor)
Chemical FormulaCaCO3 + various clay minerals
Mohs Hardness3
Crystal Systemtrigonal
Streak ColorWhite
CleavageNot distinct in bulk concretion; primary mineral calcite shows perfect rhombohedral.
FractureUneven
Specific Gravity2.7
Colorslight grey, beige, brownish-grey
TransparencyOpaque
Type LocalityTåsjön, Ångermanland, Sweden
Mineral GroupCarbonates and Silicates
Usesgeological study, collector's item
Associated Mineralscalcite, clay minerals, quartz
Rarityuncommon
Description
These are naturally occurring, often disc-shaped or irregularly formed concretions, typically light grey to beige, composed of calcareous clay.
Geological Context
Formed through the precipitation and cementation of calcium carbonate within calcareous clay sediments in flowing water, creating distinctive, often flattened or rounded shapes.
