oxydised iron

Diamonds with garnets can form at depths within Earth's Manetle. Earth scientists, it is said, made a discovery that 550km beneath the surface – oxydised iron. This is similar tro rust. It was found within garnets within diamonds – we are told. How does iron become rusty within the Mantle? One might point a finger at water in the Mantle – but not these guys. We know that iron exists as a metal in the core and Mantle – or so the mainstream songsheet assures us (and why not – a reasonable deduction). Here we have evidence that something oxydised some of the iron – in rocks in which diamonds are formed. Diamonds have an origin in carbon – was it due to carbon in rocks sinking into the Mantle as a result of Plate Tectonics (sea floor disappearing at the subduction zone). What is required to make diamonds? See https://phys.org/print435943930.html