Vivianite is a rare mineral belonging to the iron phosphate family, prized for its crystals with intense green hues that naturally evolve to a deep, almost black blue. This collector's stone is distinguished by its unique chromatic evolution: upon contact with air, the iron it contains gradually oxidizes, revealing fascinating dark shades.

Crystallizing in elongated prisms or rosettes, vivianite is particularly sought after by collectors and enthusiasts of rare minerals.