Death and decay can produce the most amazing of results. If my foraminifera die in, and perhaps because of, oxygen-free conditions, they would decay, which would release sulphur, which in turn can react with present iron to ison sulfides such as iron disulfide. Also known as pyrite! And that is also knwn as fool's gold; this name gives an indication of its prettiness. So if all the forams in your sample you stare at through a microscope have turned to pyrite, it looks like you're looking into a shop window close to christmas. There are worse ways of spending your working hours!