When walking in old woodland with lots of fallen branches and twigs you may encounter a piece of rotting wood with a metallic green appearance. It is easy to pass this by thinking it is just natural colouration but it is, in fact, produced by a fungus, Chlorociboria aeruginascens. The fungus does produce fruiting 'cups' later in the year although these are small and rarely seen and, of course, the fungus itself which lives inside the rotting timber may not be seen until the wood starts to break up.
The Chlorociboria fungus particularly infects oak and the resulting effect is sometimes called green oak and is used in marquetry and other wood working techniques to give a green/blue appearance to the finished product. This is very common, often over looked, and sometimes not visible but it worth keeping an eye out for as it looks really lovely, especially in good light.
I think you might break your teeth if you tried to eat it!Chlorociboria aeruginascens: the green elf cup fungus