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Article: Jet (gemstone)

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.

Locations of Jet Deposits

  • 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.

History of Jet

  • 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.

Jet Substitutes

  • 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.

Authenticating Jet

  • 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.

See also:

  • Petrified wood.
  • Oltu stone.


  • 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.

Jet (gemstone) Data Sources

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