Jade is an ornamental rock. The term jade is applied to two different metamorphic rocks that are composed of different silicate minerals: nephrite and jadeite. Nephrite and jadeite were used from prehistoric periods for hardstone carving. Jadeite has about the same hardness as quartz. Nephrite is slightly softer, but is tougher (more resistant to breakage) than jadeite.
Imitation Rhodium uses a similar-looking material to substitute for rhodium. It makes the jewelry more affordable, but at the same time keeps the same appearance and quality as a rhodium coating.