Jet is fossilized wood, a less brittle type of lignite coal. It has an organic origin, therefore, it’s not a mineral. It’s considered a gem, like amber and pearl is. Jet will burn like coal, releasing an oily odor, whereas plastic imitations will have an acrid smell.
Jewelry made of Jet dates back to Neolithic times in Ancient Britain. Later the Ancient Romans popularized Jet for ornamental use and its 'magical properties'. Taking after Queen Victoria, during the Victorian Era, jet jewelry became a popular to wear while mourning.
Clean with a mild detergent using soft brush and warm water.