Whitby Jet

Whitby Jet, or the classical English gemstone famed from Victorian-era mourning jewellery, has been misclassified for many years as a type of coal (often classified as a lignite), but this is not exactly the case.

Whitby Jet is follised (or 'jetonised') driftwood from the Toarcian period of the Lower Jurassic (183 million years ago). It was formed during a period of extreme climate change (leading to the seventh-largest extinction event in the geological record) called the Toarcian Oceanic Anoxic Event. These conditions promoted bacterial and algal blooms in the bottom-waters of the Cleveland Basin, their byproducts being organic molecules which impregnated the driftwood during early diagenesis leading to the material we now call Whitby Jet.

Older suggestions that Whitby Jet originated from wood of the Monkey Puzzle Tree (or Araucaria) have also been disproven, with analysis showing six or more different species of tree being the source, none of them being Araucaria.