# Jet

- Page: https://taslar.bumba.tr/en/stones/jet/
- Turkish: Jet
- Also known as: Gagates (ancient Greek and Latin name), Azabache (Spanish), Jais (French), Gagat (German)
- Kind: Organic gem
- Classification: Organic gems
- Crystal system: Amorphous (no crystal structure)
- Hardness (Mohs): 2.5–4
- Specific gravity: 1.3–1.4 g/cm³
- Refractive index: 1.66
- Lustre: Greasy, Vitreous (glassy), Dull
- Transparency: Opaque
- Colours: black, dark brown
- Streak: Brown
- Cleavage: None
- Fracture: Conchoidal (shell-like)
- Composition: Coalified wood: roughly 75% carbon and 12% oxygen, with sulfur and hydrogen making up most of the rest. Counted as a dense, fine-grained kind of lignite or sub-bituminous coal; sometimes contains brassy pyrite inclusions.
- Texture: A compact, uniform mass with no crystal structure; unlike coal it is not laminated and has no network of cracks. It turns easily on a lathe and takes a high polish.
- Value ladder: 6/9 step, Fine ornamental and collector stone

Wood that sank, was buried and turned to coal millions of years ago: a light, glossy black organic gem, worn in Whitby's mourning jewellery and Oltu's prayer beads.

Jet is a black stone formed when pieces of wood from ancient trees were buried in mud at the bottom of the sea or a lake and slowly turned to coal over millions of years. It belongs to the coal family, but unlike ordinary coal it does not crumble: its compact structure lets it be carved and turned on a lathe, and it takes a mirror-like polish. Because it has no crystal structure and comes from a living thing, it is classed as an organic gem rather than a mineral. In Türkiye, the jet from Erzurum is called Oltu stone.

## How does it form?

Jet is a kind of **coal** formed from wood; in rank it lies between lignite and sub-bituminous coal. But it does not form from the broad swamp layers that make coal seams. It forms from individual pieces of wood: branches and trunks broken off trees became waterlogged, sank to the bottom of the sea or a lake and were covered by mud rich in organic matter. As they were buried deeper, the wood was flattened and coalified by rising heat and pressure, and at the same time it soaked up oily substances (bitumen) from the decaying algae and plankton around it. That is why jet has a compact, uniform texture without the network of cracks seen in coal.

Jet formed in salt water is called **hard jet**, and jet formed in fresh water **soft jet**. Both have the same range of hardness, but soft jet cracks more easily when the temperature changes. Whitby jet formed in the Early Jurassic, about 181–183 million years ago, from the wood of trees resembling the araucaria family.

## What is it used for?

- **Jewellery and ornaments:** beads, necklaces, rings, bracelets, brooches, hairpins, cameos and buttons. It turns easily on a lathe and takes a high polish.
- **Prehistory and Rome:** in Britain it was used for necklace beads from the Neolithic to the Bronze Age. In Roman Britain, from the 3rd century, workshops in York made rings, bracelets and pendants carved with Medusa heads.
- **Religious objects:** in the Middle Ages it was used mostly for crosses and rosaries. In Spain, Santiago de Compostela became famous for craftsmen who made jet amulets and devotional objects for pilgrims on the Camino de Santiago.
- **Mourning jewellery:** after Prince Albert died in 1861, Queen Victoria wore Whitby jet with her mourning dress, and jet became the favourite mourning jewellery of the 19th century.

## Where is it found?

The most famous source is **Whitby** on England's north-east coast; the deposits extend across the North York Moors, and jet was once gathered on the beach or mined from galleries cut into the cliffs. The Jurassic coast of **Asturias** in Spain, especially Oles near Villaviciosa, is Europe's other famous source, and lower-quality jet comes from Teruel. In the 18th century the Aude region of France had a jet industry. Jet also occurs around Holzmaden in Germany and in Utah, Colorado and New Mexico in the United States.

## In Türkiye

Türkiye's jet is **[Oltu stone](/en/stones/oltu-stone/)** from the Oltu district of Erzurum: it is mined by hand from narrow galleries and used above all for prayer beads. The name of jet itself has its roots in Anatolia: in ancient Greek and Latin the stone was called “gagates” after the Lycian town of **Gagae** and the nearby river Gages. The ruins of Gagae lie in today's Kumluca district of Antalya, but the deposit described by ancient writers has not yet been found. The French word “jais” and the English “jet” both derive from this name.

## How to recognise it

- It is very light (specific gravity about 1.3–1.4): a piece of black glass or onyx the same size weighs about twice as much. It feels warm rather than cold in the hand.
- Rubbed on unglazed porcelain or fine sandpaper it leaves a brown streak; black glass does not.
- It is soft (Mohs 2.5–4), so a steel needle can scratch it. It breaks with a curved, glossy, shell-like fracture, and like amber it becomes charged when rubbed on wool.
- Do not use the hot-needle test: it damages the piece, and some old celluloid imitations contain nitrocellulose, an ingredient of gunpowder, and can catch fire. A reliable identification needs laboratory testing.

## Fakes and imitations

- French jet: the black glass used in place of jet in the 19th century; it is not jet at all. It is noticeably heavier, feels cold and leaves no brown streak.
- Ebonite (vulcanite): rubber hardened with sulfur. It looks very like jet at first, but over time it fades to a khaki or brownish tone.
- Anthracite, bog oak and lignite: these can also leave a brown streak; well-polished anthracite is especially hard to tell from jet.
- Bakelite, celluloid and other plastics, and “pressed” pieces moulded from jet offcuts mixed with glue, may also be sold as jet.

## What determines its value?

The value of jet depends first on its hardness and stability: “hard jet”, formed in salt water, is far more sought after than “soft jet”, which tends to crack over time. A deep, even black, a piece free of cracks and inclusions, and a good polish add value. The fame of the source matters too, with Whitby and Asturian jet the best known. In antique pieces, craftsmanship, age and historical context (Victorian mourning jewellery, for example) often count for more than the stone itself, while imitations in glass, ebonite or plastic are worth very little.

This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.

## Myths and misconceptions

- Myth: Jet is a kind of black amber. Fact: Amber is fossilised tree resin, whereas jet is coalified wood. Both are light, organic and become charged when rubbed, which is where the name “black amber” comes from, but it is misleading.
- Myth: Whitby jet is fossilised monkey puzzle tree (Chilean pine). Fact: This is a Victorian misconception. Whitby jet comes from ancient trees related to the araucaria family, but the wood cells were so squashed by pressure that the species cannot be identified with certainty; researchers have described two kinds of fossil wood of the genus Dadoxylon.
- Myth: “French jet” is a kind of jet mined in France. Fact: French jet is the trade name of the black glass used in place of jet when jet was fashionable in the 19th century. Real jet has been mined in France too, but this name describes glass.

## What is it believed to be good for?

This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.

- Ancient writers such as the Roman author Pliny and the physician Galen recorded beliefs that the smoke of burning gagates, or jet, drove away snakes, revealed epilepsy and helped with women's ailments.
- In Roman times, amulets and pendants made of jet were believed to protect the wearer from the evil eye.
- In medieval Europe, water drunk from a bowl made of jet was believed to ease childbirth.
- In Spain and in Spanish-speaking communities such as those of Puerto Rico, Cuba and the Dominican Republic, a small jet (azabache) fist amulet worn by babies is believed to protect them from the evil eye and from disease, even from sudden infant death.

What science says: There is no scientific evidence that jet prevents or cures any illness. The ancient use of its smoke comes from the fact that jet burns like coal, and breathing coal smoke is harmful. Small amulets and beads worn by babies carry a risk of being swallowed or causing choking. The way to reduce the risk of sudden infant death is the safe-sleep practice recommended by doctors, not an amulet.

## Did you know?

- The English word “jet-black” comes from the name of this stone.
- The oldest known worked piece of jet dates to about 10,000 BC: a small figure resembling a botfly larva, found in the Petersfels cave in Baden-Württemberg, Germany.
- Whitby's jet industry peaked between 1860 and 1880, when more than 200 workshops employed about 1,500 people. Only eight jet makers remain in the town today, and the craft is listed as “critically endangered”.

## Where is it found?

- Whitby, North Yorkshire, England (Major deposit): Whitby jet, about 181–183 million years old (Early Jurassic), is counted as the world's most famous and finest jet; the deposits extend across the North York Moors.
- Oles, Villaviciosa, Asturias, Spain (Major deposit): The jet (azabache) deposits of Asturias's Jurassic coast; northern Spain's largest deposit is about 155 million years old. No mine is open today, and craftsmen gather the stone from old spoil heaps and cliffs.
- Utrillas, Teruel, Spain (Known locality): Jet deposits of Teruel province (Utrillas, Gargallo, Montalbán); of lower quality than Asturian jet.
- Sainte-Colombe-sur-l'Hers, Aude, France (Historic source): An 18th-century jet (jais) working industry flourished around Sainte-Colombe-sur-l'Hers and La Bastide-sur-l'Hers; it declined in the 19th century.
- Holzmaden, Baden-Württemberg, Germany (Known locality): Jet (German Gagat) in the roughly 180-million-year-old Posidonia Shale, the same age as Whitby jet.
- Henry Mountains, Utah, USA (Known locality): One of the places in the USA where jet is known; it also occurs in Colorado's Front Range and in New Mexico.
- Oltu, Erzurum, Türkiye (Major deposit): The jet found here is called Oltu stone; it is mined by hand from narrow galleries in villages north-east of the town and used for prayer beads.
- Ancient Gagae, Kumluca, Antalya, Türkiye (Historic source): Jet's ancient name, gagates, comes from this Lycian town and the nearby river Gages. Ancient writers say the stone was found at the river mouth, but the location of the deposit is unknown today.

## Sources

- [Jet (gemstone)](https://en.wikipedia.org/wiki/Jet_(gemstone)), Wikipedia
- [Jet](https://www.britannica.com/topic/jet-gemstone), Encyclopaedia Britannica
- [Jet: The Gem Made From Fossilized Wood](https://geology.com/gemstones/jet/), Geology.com
- [Whitby Jet and Jet Jewellery](https://www.whitbymuseum.org.uk/collections/jet/), Whitby Museum
- [Gagat](https://de.wikipedia.org/wiki/Gagat), Wikipedia (German)
- [Azabache](https://es.wikipedia.org/wiki/Azabache), Wikipedia (Spanish)
- [Gagae](https://en.wikipedia.org/wiki/Gagae), Wikipedia
- [Remarks on the Beds and Areas of Use of a Gem Reputed in Antiquity (F. Onur), ADALYA](https://avesis.akdeniz.edu.tr/yayin/258588e2-9097-49be-85fb-d55014a5df07/remarks-on-the-beds-and-areas-of-use-of-a-gem-reputed-in-antiquity), Suna & İnan Kıraç Research Institute on Mediterranean Civilizations, 2011
- [A Hispanic amulet against disease in infants (E. Tabor), Hektoen International](https://hekint.org/?p=41389), Hektoen Institute of Medicine, 2023
- [Oles (Villaviciosa)](https://en.wikipedia.org/wiki/Oles_(Villaviciosa)), Wikipedia
- [Utrillas](https://en.wikipedia.org/wiki/Utrillas), Wikipedia
- [Holzmaden](https://en.wikipedia.org/wiki/Holzmaden), Wikipedia
- [Oltu Taşı — Coğrafi İşaret Tescil Belgesi (No. 192)](https://ci.turkpatent.gov.tr/Files/GeographicalSigns/192.pdf), TÜRKPATENT, 2012


Source: https://taslar.bumba.tr/en/stones/jet/ · Licence: CC BY-SA 4.0