The Gemstone Called Jet

Carved Natural Jet

The term "jet black" in English refers to a very dark shade of black. But what's the connection between the color black and jet airplanes? Were the first jets painted black? Or does it have to do with the color of the exhaust from a jet engine?

The answer is actually found in the history of gemstones, rather than details of the technology of aviation. The term "jet" in the expression "jet black" refers to a gemstone material that was very popular in the nineteenth century, but is hardly heard of today.

Jet is an organic material composed of fossilized wood. A form of bituminous coal, jet can be polished to produce a waxy, velvety luster.

Jet was known to the Romans. They called it gagates, from the Greek gagates lithos, meaning 'stone of Gages', a town and river in Lycia. The Greeks valued the mineral, and believed that powdered jet mixed with wine would prevent toothache. When mixed with beeswax, they believed that jet was a remedy for tumors, and burned as incense it was supposed to drive away devils.

Jet as a gem material was especially popular during the reign of Queen Victoria. The Queen wore jet mined in Whitby, Yorkshire, as part of her mourning dress after the death of her husband, Prince Albert. Jet was popular for mourning jewelry because of its somber color and modest appearance, and it has also been traditionally fashioned into rosaries.

Jet has a very low density, so it is suitable for large pieces of jewelry. But it is also quite soft compared to most gemstones, with a hardness of only 2.5 to 4.0 on the Mohs scale. Jet is now unfashionable, probably because of its association with mourning.

Of course, black is still a stylish color for gemstones. But other black gemstones have now taken the place of jet. The most common is onyx, a variety of chalcedony or cryptocrystalline quartz, which is dyed to produce a uniform black. Onyx is abundant and inexpensive. Some finer gems are occasionally found in black, such as diamond, sapphire and spinel. But the most easily available, high quality black gemstone is tourmaline. Also known by the name schorl, black tourmaline is the most common form of this remarkable mineral. Perhaps 95% of the tourmaline found in nature is black, and this is why black tourmaline is relatively inexpensive, selling at reasonable prices that are below those of amethyst or citrine.