Jet is an opaque black fossil plant material. Found in coal seams that were laid down in ocean water. The petrification of the ancient plants in the salt formed a very tough resinous fossil rock.
Jet can be cut and polished into a lustrous and semi-precious stone which can be used for carving, inlaying jewellery, and ornaments.
“The Black Queen” of Victorian jewellery, the best jet can be found in Whitby, England.