Banded iron formations (BIFs) contain well developed iron-rich thin alternating layers or laminations as seen here.

In the beginning, there was no oxygen, and iron dissolved in the oceans. When photosynthesis got going, oxygen began to accumulate in the atmosphere and oceans. Some of the dissolved iron oxidised – rusted – and precipitated to the sea floor. Sedimentary layers of iron covered the bottom of the oceans making some of the most stunning and colourful geological records.The name comes from the various coloured layers.

This work was made for an exhibition on the theme of photosynthesis at the Royal Institution in London. As distinctive units of sedimentary rock that are almost always of Precambrian age, banded iron formations certainly predate the creation of the Royal Institution. But the connections of the Ri with photosynthesis and with light in a wider sense are many over the years.