T288 Gemological Research in the 21st Century—Gem Minerals and Localities

Wednesday, 25 September 2019
1:30 PM - 5:30 PM
Room 132ABC, North Building

JET: A JURASSIC PLASTIC LOST IN THE ANTHROPOCENE?

Paper number: T288-13
Program: Technical Sessions
Time: 4:30 PM – 4:45 PM

Authors

Abstract

Defined by Stach (1927) as ‘being formed from drifted wood which has been secondarily impregnated with bitumen’, gem quality hydrocarbons known as ‘jet’ have been utilised for high-status ornamentation since the Upper Palaeolithic. Despite representing a socio-symbolically significant resource, little progress has occurred in the characterisation and provenancing of this material.

Requiring an increase in atmospheric carbon, global warming and oceanic anoxia, the paleo-environmental conditions required for the jetification of wood have seldom occurred in earths geological history. The resulting material displays distinct polymeric properties; low specific gravity, low thermal conductivity, triboelectricity and combustibility. As such it can perhaps be described as a ‘Jurassic plastic’.

During periods of high demand, we see many carbonaceous materials, plus natural and semi-synthetic polymers used as jet simulants. When presenting as polished objects, these black, opaque materials are visually difficult to distinguish, yet discrimination is important for understanding exchange, due to the restricted geospatial occurrence of jet.

An unprecedented demand for jet in the C19th led to a depletion of natural reserves and a quest for new simulants. These materials needed to share the ‘plastic’ properties of jet. Baekeland’s 1907 creation of phenol formaldehyde patented as ‘Bakelite’, was actively retailed as jet until the 1940’s. His material not only shared the qualities of jet, but he claimed to have surpassed nature. We, as a race he said, had entered the Fourth Kingdom, we had created a new material under the sun.

The fate of jet as a gem material has been shown to mirror the fate of modern plastics. Initially a luxury commodity, once available to a mass market its worth depreciated. Despite the odds, and testament to the 1980’s slogan, jet has survived as a gem product. Proof, if we needed it, that “plastic is forever and a lot cheaper than diamond”.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-340191

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