Different Bark textures on Whitby Jet

Whitby Jet Samples with fossilised bark

What is Jet?

A simple enough question with a rather complicated answer! 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. Peat naturally contains animal, vegetable and mineral matter. Jet, however, is formed from individual logs and in aquatic environments, usually marine and not formed on land as in the case of fuel-grade coals. The Geology Read more  If however, we 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. Sarah has recently returned to Durham University as a postgraduate researcher. Her project is essentially designed to understand the geo-archaeology and archaeo-gemmology of these black materials and at reclassifying 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, Bakerlite and Lucite. Most families have hidden somewhere a collection of black jewellery handed down through the generations and simply termed ‘Granny’s Jet’. The Simulants Read more 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. Read more Advanced Jet testing

So what really is it?

Well, it is indeed formed from the fossilisation of wood but unlike most coal which is fossilised peat bog and contains animal, vegetable and mineral matter, Whitby jet is a result of individual logs being preserved in a marine environment. Wood cannot become jet however without very specific paleoenvironmental conditions. These hostile conditions promote the formation of oil and this is crucial to the formation of our gem material.

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