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See our: jet jewelry.
A compact, velvet-black substance that is a variety of lignite or coal, being formed by pressure, heat and chemical action on ancient driftwood. It has a glossy brownish-black surface and a black interior.
There are two varieties, hard jet and soft jet, of equal hardness but the latter, more recent, being more fragile and so less often used in jewelry; even hard jet is easily broken, and so jet articles, when skillfully carved, were expensive.
Its principal source in ancient times (examples are known from the British Iron Age) and in Roman times and thereafter was the Liassic shales of the Yorkshire coast near Whitby, England, whence jet was mined and shipped to Rome during the Roman occupation. Whitby became the centre of the jet industry from c. 1808 to c. 1875, after which jet was largely superseded by chalcedony that was dyed black (sometimes called 'black onyx'), as well as by black tourmaline (schorl) and black andradite (melanite).
Jet can be effectively carved, engraved, faceted, and highly polished, so was extensively used for mourning jewelry and buttons, and consequently was popular in England after the death of Prince Albert (1861). It was made into earrings, finger rings, beads, pendants, brooches, and lockets. It can be distinguished from black gemstones and from glass and plastic imitations by touching it with a heated needle (this releases an odour of burning coal).
An inferior quality of jet has been produced in Galicia, northern Spain, and used there extensively for making amulets, especially for the 15th-century pilgrims to Santiago de Compostela. The present source of jet is still the Whitby region.
See also: French jet
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson