Dark patterns on a beach in shallow waters that are a classic example of heavy mineral sorting (often called a "placer" formation). Heavy Mineral Streaks: The dark purplish-black areas are concentrated deposits of heavy minerals (magnetite, ilmenite, garnet). Light Mineral Patches: The beige/tan areas are the lighter quartz and feldspar sands. Flow Patterns: The sand is sculpted into fluid, wavy shapes ("swash marks"), showing exactly where water flowed and separated the grains based on density. Sestroretsk near St.Petersburg, Russia

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