Jet (gemstone)

Origin and Properties of Jet

Jet is a product of decomposition of wood from millions of years ago, commonly the wood of trees of the family Araucariaceae.
Jet is found in two forms, hard and soft.
Hard jet is the result of carbon compression and salt water; soft jet may be the result of carbon compression and fresh water.
Both hard and soft jet occupy the same area of the Mohs scale, but soft jet is more likely to crack when exposed to changes in temperature.
Jet is around 75% carbon and 12% oxygen, with sulfur and hydrogen making up most of the balance.
The exact ratios of other elements found in jet vary with the source.
Jet has a Mohs hardness ranging between 2.5 and 4 and a specific gravity of 1.30 to 1.34.
The refractive index of jet is approximately 1.66.
Jet may induce an electric charge like that of amber when rubbed.

England:
Whitby, England, is known for its jet deposit, which was formed approximately 181 million years ago.
Whitby Jet is fossilized wood from species similar to the extant Chilean pine.
The jet deposit extends throughout North York Moors National Park.
Jet has also been found in Kimmeridge shale seams in Dorset.
France:
Jet was mined from areas such as Montjardin and Roquevaire.
Raw jet was imported from Spain.
In the 18th century, there was a jet working industry based around Sainte-Colombe-sur-lHers and La Bastide-sur-lHers.
An 1871 plan to import raw French jet into Whitby was unsuccessful due to its poor quality.
Spain:
The biggest jet deposit in northern Spain is found in Asturias and is approximately 155 million years old.
Jet is also found near Santiago de Compostela in northwest Spain.
United States:
Native American tribes in New Mexico, such as the Navajo and Pueblo, used regionally mined jet for jewelry and ornamentation.
Jet deposits can be found in the San Juan Basin of New Mexico and the Henry Mountains of Utah.
Jet deposits are also found in the Front Range of El Paso County, Colorado.
Other locations:
Jet is commercialized in Poland.
Jet is found near Erzurum in Turkey, where it is known as oltu stone and used to make prayer beads.

The earliest known worked jet object is a 10,000 BC model of a botfly larva from Germany.
Jet has been used in Britain since the Neolithic period and continued through the Bronze Age.
During the Iron Age, jet went out of fashion until the early 3rd century AD in Roman Britain.
Early archaeologists often failed to distinguish between jet and other jet-like materials, such as Kimmeridge Shale.
Jet was popular for jewelry in Roman Britain and was used in various forms such as rings, hair pins, beads, and pendants.
Vikings made use of jet, including rings and miniature sculptures of animals.
The source of the jet used by Vikings is likely Whitby.
Snakes were a prominent theme in Viking jet sculptures.

Glass used as a jet substitute during the peak of jet's popularity, known as French jet or Vauxhall glass.
Ebonite also used as a jet substitute, but fades over time.
Jet offcuts mixed with glue and molded into jewelry.
Anthracite (hard coal) used to imitate jet, difficult to distinguish from real jet.
Museums producing reproductions of jet artifacts in epoxy resin.

Jet is not cool to the touch, unlike black glass.
True jet leaves a brown streak when rubbed against unglazed porcelain.
X-ray fluorescence spectroscopy combined with visual inspection and X-ray imaging effective for non-destructive testing.
Real jet burns like coal, giving off a coal-like smell and producing soot.
No other black gemstone behaves like jet when exposed to flame.

Neuendorf, K. K. E. Jr.; Mehl, J. P.; Jackson, J. A., eds. (2005). Glossary of Geology.
Holmes, Ralph J.; Crowningshield, Robert (1983). Gemology.
Oxford English Dictionary (2nd edition) 1989.
Pye, K. (1985). Electron microscope analysis of zoned dolomite rhombs in the Jet Rock Formation.
Muller, Helen; Muller, Katy (2009). Whitby Jet.

Reference	URL
Glossary	https://harryandcojewellery.com.au/blogs/glossary/jet-gemstone
Wikipedia	http://en.wikipedia.org/wiki/Jet_(gemstone)
Wikidata	https://www.wikidata.org/wiki/Q543694
Knowledge Graph	https://www.google.com/search?kgmid=/m/02qkkn