Jet was very popular in Victorian times, and is basically fossilized bog oak that was carved and polished. The black material became widely used during Queen Victoria’s many years of deep mourning. It was also copied, using polished, faceted opaque black glass, which was often referred to as French jet.
Kara Ross’s web site gives little information about this piece, and so I don’t know if this is real jet, or another substance made to look like jet. No prices on her web site but she is sold at the stores listed here.