Williamsite is a semi-transparent to translucent variety of antigorite, a mineral in the serpentine group. Williamsite was named in honor of 19th century American mineral collector L.W. Williams, who first discovered it. With a range of green hues, its color has a marked resemblance to two more expensive gems, jade and chrysoprase, and is used as a simulant of both. Williamsite exhibits an oily luster when polished and often contains minor inclusions of chromite and magnetite.