This image shows the crystalline structure of vivianite, captured using scanning electron microscopy (SEM).
Vivianite (Fe3(PO4)2·8H2O) is a mineral that forms in anoxic environments, or rather, waterlogged soils with poor oxygen levels and sources of iron and phosphate. The conditions at Vindolanda promote vivianite formation. Vivianite is colourless until exposure to oxygen, when it quickly becomes a pale blue colour. TUBA is investigating why vivianite is so effective at preserving material excavated at Vindolanda.