Gold-plated, wide-hammered cuff with jet accent. Photo by April M. Licensed under CC By-ND 2.0.
Historically a popular black gem, jet has declined in popularity in modern times. Although jet jewelry has been long associated with mourning, this organic gem can be made into large, eye-catching beads, carvings, and even faceted pieces.
| Data | Value |
|---|---|
| Name | Jet |
| Crystallography | Amorphous. Usually in coal seams as black masses and lumps. |
| Refractive Index | 1.66 |
| Colors | Black, brownish. |
| Luster | Dull, Waxy. |
| Polish Luster | Vitreous. |
| Hardness | 2.5-4 |
| Fracture | Conchoidal |
| Specific Gravity | 1.19-1.35 |
| Birefringence | None |
| Cleavage | None |
| Dispersion | None |
| Transparency | Opaque. |
| Formula | C. (Carbon, plus impurities). |
| Pleochroism | None. |
| Optics | Blurred shadow edge on refractometer at 1.66. |
| Etymology | From the Greek Gagae, the name of a town and river in Asia Minor, now Turkey. |
| Occurrence | Jet is fossilized wood, a form of lignite brown coal. |
Jet, Whitby, England. Photo © Joel E. Arem, PhD, FGA. Used with permission.
The use of jet jewelry dates back to Neolithic times in Ancient Britain. The Ancient Romans later adopted and popularized this gem material not only for ornamental use but for its purported magical properties.
Jet pendant with undeciphered magical script on one side and an animal image on the other (2.3 x 4.3 cm). Excavated in Nishapur, Iran, 9th-10th centuries CE. Rogers Fund, 1940. Public domain. Metropolitan Museum of Art, New York. Public Domain.
During the later Victorian Era, jet jewelry became a popular choice for mourning wear, after the style of Queen Victoria herself.
Victorian carved jet mourning brooch. Photo courtesy of liveauctioneers.com and Florida Estate Sales, Inc.
Jet is a variety of lignite coal. It forms from fossilized wood. Since it has an organic origin, it’s not a mineral. Nevertheless, it’s considered a gem, like amber and pearl. Although jet resembles anthracite coal, it’s less brittle
Jet takes a very good polish. Faceting can add some sparkle to the somber tones of jet jewelry. (Gemstones often have a flat bottom).
Faceted jets: Whitby, England (~ 3 cts each). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Not surprisingly, jet burns like coal. A hot point test will release an oily odor. (Plastic imitations will release an acrid smell). Keep in mind this destructive test should only be used as a last resort for gem identification. Choose an inconspicuous spot to test any finished gem or jewelry piece.
In addition to plastic, black glass can simulate jet gems. However, true jet is warmer to the touch than glass. “French Jet” was a popular glass imitation during jet’s 19th century heyday. Natural gemstones that may be substituted or confused with jet include obsidian, black tourmaline, and chalcedony.
D&E Juliana Marquise French Jet and clear rhinestone butterfly brooch. Photo by GlitzUK. Licensed under CC By-ND 2.0.
Whitby, England yields the finest jet in seams. Spain also produces a harder but more brittle variety. Most commercial material comes from these locations.
“Whitby Jet, straight from the beach,” photo by S0MEBODY 3LSE. Licensed under CC by 2.0.
Other notable sources include the following:
Jets, Oltu District, Erzurum Province, Turkey, largest specimen 65 x 30 x 35 mm. Photo by Erik Vercammen. Licensed under CC By 3.0.
Due to jet’s relatively low density, gem cutters can fashion carvings, cabochons, and objects either decorative or utilitarian in almost any size desired.
Jet is brittle and has a relatively low hardness. Thus, jet jewelry such as rings or other pieces for frequent wear should have protective settings. Store jet separately from other harder materials to prevent contact scratches. Avoid mechanical cleaning systems such as ultrasonic or steam. Use a soft brush, mild detergent, and warm water for cleaning. Consult our gemstone jewelry cleaning guide for more recommendations.
Jet oval pendant with man and woman, circa 43-410 CE, Yorkshire Museum, York, England. Photo by York Museums Trust Staff. Licensed under CC By-SA 4.0.
Turkey’s gemstones include well-known species such as diaspore, chalcedony, and jade, as well as unusual specimens of lesser-known gems. Learn…
IGS Become Member