If you’ve ever heard that someone has “jet black” hair, it means that their hair is as black as this organic “mineraloid” (like a mineral…but not really a mineral). Jet is a particular type of coal that comes from wood that’s been transformed into mostly carbon over millions of years. Though jet is kind of the opposite of anthracite coal, since it’s the lowest grade of coal, it’s still solid enough that it can be nicely polished and used in jewelry. It can also be carved pretty easily, given its low hardness, and has been used to make carvings since ancient times, long before steel tools were invented. Although it had special meaning to the Vikings and Romans, it’s probably most well known for being used in “mourning jewelry” during the Victorian Era, which lasted from 1837 to 1901. During that time, women whose husbands, children, or other family members had died would wear black jewelry, which was often made of jet, in memory of those who had passed on.