What is Whitby jet?
“What is Whitby Jet?”, is probably the most frequently asked question in Whitby! Jet information available online is often confusing and more often than not, is completely incorrect for example, the monkey puzzle myth. I shan’t go into that here but you can learn the truth here Is Whitby Jet Monkey Puzzle wood? When I began researching the subject some 20+ years ago I discovered rather quickly that the term ‘jet’ means quite a different thing to different groups of people. If I ask geologists, they will say that it is an unusual fossilisation of wood. A type of coal perhaps? Jet however unlike most coals is not formed from a fossilised peat bog, rather, it is formed from isolated masses of fossilised driftwood.
If however, I ask archaeologists, they use the generic term ‘jet-like materials’ to describe black carbonaceous finds in the archaeological record. This includes materials such as oil-shales, cannel coals and bog-oak. Although archaeologists are aware of the problem with distinguishing it from other materials, there has been little progress in this field of research. My current PhD research project is essentially designed to understand the geo-archaeology and archaeo-gemmology of these black materials and to reclassify and identifying these materials correctly.
If we ask the question to the jewellery trade, is used as a generic term to cover all Victorian mourning jewellery. These include glass, horn, vulcanite, other early plastics such as Galalith, Bakelite and Lucite. Most families have hidden somewhere a collection of black jewellery handed down through the generations and simply termed ‘Granny’s Jet’.
Gemmologist consider jet to be an organic gemstone in the same class as amber, pearl, ivory and horn. This is way too simplistic and in my opinion, the group of materials require an overhaul from a descriptive perspective. Jet can also be described as a ‘biogenic’ material but this too is not the full story. I am currently working on a branch of gemmology called “Hydrocarbon Gemmology” to better classify the black, opaque members of the organic gemstone group.
What I can tell you is that Whitby jet is actually fossilised driftwood from the Toarcian Period of the Lower Jurassic.The rocks containing the Whitby jet began to be deposited 183 million years ago. This was a period of extreme climate change and the resulting conditions led to perfect conditions for the jetonisation of wood. The conditions in the oceans, however, were not so good for animal life and at the beginning of this sequence of deposition the rocks bear witness to the seventh-largest extinction event in the geological record. This catastrophic event is known as ‘The Toarcian Oceanic Anoxic Event (TOAE) and is the first period of oceanic anoxia witnessed in the geological record. As a result, the strata containing the jet has been of great interest to the scientific community especially as certain areas of our modern oceans are beginning to show the early signs of anoxia. Many of the unique properties of our Whitby jet are as a result of these toxic conditions which promoted bacterial and algal blooms in the bottom waters of the Cleveland Basin. These microorganisms produce byproducts in the form of organic molecules which impregnated the driftwood during early diagenesis giving us the intensely black, lustrous material we know today as jet.
Unlike most fossilised wood, jet is formed by the ‘jetonisation’ rather than ‘petrification’ of the wood. Jet is therefore preserved as a hydrocarbon rather than replaced by minerals. It is way too simplistic to class Whitby jet as coal, as the formation is completely different from most fuel-grade coals. Whitby jet does, however, share the properties of coals in regards to combustion.
It is often quoted that jet is formed due to heat and pressure, this, however, is incorrect as the formation of coals including jet, is hindered by extreme pressure. Jet actually forms due to unusual chemical bonding within the matrix of the material which leads to an abnormal concentration of hydrogen. Jet also has other qualities which make it unusual from a hydrocarbon perspective, namely its supreme stability in regards to an oxygen-rich environment. The stability means that we find archaeological finds, made from jet which are still pristine some 5,500 years after they were made.
Coals, which are generally formed as a result of the fossilisation of a whole forest, contain remains of everything that was living in that community and therefore comprise of matter which is animal, vegetable and mineral. Jet, however, is formed from individual planks of driftwood. These pieces although referred to as ‘planks’ range in size from small twigs to whole tree trunks. Likewise, although us jet workers often refer to ‘seams’ of jet, this is not actually true. Jet, unlike commercial fuel-grade coals, does not form in seams but in individual planks distributed over an eight-mile outcrop around Whitby. The intense black colour of jet, its deep lustre, ease of polish, low specific gravity and triboelectric properties have led to it being used as a decorative product for 5,500 years.
My aim is to classify the whole Jet Group of gemstones in order to better understand and ultimately protect these ancient gem materials and those peoples who work them as a way of life.