Jadeite is one of the two varieties of the stone called
jade. Most
gemstone experts consider jadeite to be the only gem-quality jade, and it costs much more than the other variety,
nephrite because it is finer (less grainy) and more
translucent than nephrite. The best quality jadeite comes from
Burma, but it is found in other parts of
Asia and in
Mexico and
South America.
Wintersweet tells me that jadeite is almost never the type of jade referred to in
Chinese literature and art -- it's usually
nephrite.
Jadeite can be found in green, white, charcoal gray, red, golden yellow, brown, and (in one special variety found only in mainland China), completely transparent (but this variety deteriorates quickly in exposure to air and hence isn't very useful for jewelry or carvings). The most expensive type is the emerald green color called "imperial jade" -- but since jadeite will take a dye fairly well, there is some fake imperial jade on the market. It can be identifed by examination with instruments to determine if it contains chromium, which is where real imperial jade gets its color.
Since jadeite is at best translucent, it is usually cut as cabochons or made into beads. It can be cleaned with a soft polishing cloth, or with water if you don't soak the stone for more than a few minutes at a time. Olive oil is supposed to restore the shine.