#Vivianite I had to look up last year. It is a blue-green hydrated iron phosphate (Fe2(+II)[PO4]2 x 8H2O) with monoclinic crystal structure and acicular or fibrous aggregates.

But look at this 🤩: #Vivianite pseudomorph after shell from Kerch, Crimean Peninsula, Ukraine (size: 5.6 × 4.6 × 2.7 cm). #MinCup23

📷 Rob Lavinsky, iRocks.com