Micrograph of the Month: Ferrous phosphate (vivianite)
This month we have a lovely image of a particularly colourful mineral feature called vivianite. Vivianite is an amorphous hydrated ferrous (iron) phosphate, which is blue when oxidised. It has been linked to the decomposition of bone and/or human and animal waste in wet sediments, which fits with what we know about this context. Yes, we are still looking at those waterlogged deposits from medieval Riga ! This is just one example of the many occurrences of vivianite in this layer. The small fragment of wood is also interesting. Unlike the waterlogged wood we looked at a couple of months ago , this fragment has been completely mineralised due to the presence of phosphate in the waterlogged sediment - at first glance I thought it was a bit of bone! You can also see that the pores spaces within the wood have been completely filled with fine sediments, which also indicates waterlogged conditions - the infilling of the voids occurs as fine sediments suspended in water are deposited within...