Jet

Jet is a geological material and is considered to be a minor gemstone. Jet is not considered a true mineral, but rather a mineraloid as it has an organic origin, being derived from decaying wood under extreme pressure.

The English noun "jet" derives from the French word for the same material: jaiet. Jet is either black or dark brown, but may contain pyrite inclusions, which are of brassy colour and metallic lustre. The adjective jet-black is better known perhaps than the substance from which the descriptive phrase derives.

History
Jet as a gemstone was fashionable during the reign of Queen Victoria, during which the Queen wore Whitby jet as part of her mourning dress. Jet was associated with mourning jewellery in the 19th century because of its sombre colour and modest appearance, and it has been traditionally fashioned into rosaries for monks. In the United States, long necklaces of jet beads were very popular during the 1920s, or Roaring Twenties, when women and young flappers would wear multiple strands of jet beads stretching from the neckline to the waistline. In these necklaces, the jet was strung using heavy cotton thread; small knots were made on either side of each bead to keep the beads spaced evenly, much in the same way that fine pearl necklaces are made. Jet has also been known as black amber, as it may induce an electric charge like that of amber when rubbed

Conservation
Jet is black and shiny but breaks with a conchoidal fracture. Jet is also found in England and is particularly associated with Whitby, in Yorkshire. It was much used in the Roman period for making beads etc. Jet tends to be well preserved and does not usually require any treatment after excavation.