Jade, a gemstone cut from either of two minerals-jadeite or nephrite. Jade is extremely hard. It is often elaborately carved and highly polished. The name comes from the Spanish, piedra de la ijada, meaning loin stone, so called because people once believed jade could cure kidney disorders.
Jadeite, a member of the pyroxene family of minerals, is crystalline in structure and has a glasslike luster. It comes in a wide range of colors—white, yellow, violet, and many shades of green. Jade cut from emerald green jadeite is considered one of the most valuable gemstones. Jadeite is used chiefly for ornaments and jewelry.
Nephrite, a form of amphibole, is more translucent and less crystalline than jadeite. It may be white, pale green, dark green, or black. There are two kinds of nephrite—actinolite and tremolite. Both are used for art objects and jewelry.
Jade ornaments, weapons, and utensils have been found among the relics of the Swiss lake dwellers and other primitive peoples. Jade was also known to the early civilizations of Mexico, Central America, and New Zealand. Numerous exquisite jade carvings of useful and ornamental objects were made by the Chinese as early as 1100 B.C.
Jadeite is NaAlSi2O6, with a hardness of 6.5-7. Actinolite, Ca2(Mg,Fe)5Si8O22(OH)2, and tremolite, Ca2Mg5Si8O22(OH)2, have a hardness of 5.5-6.5.