The term jade is applied to two different rocks that are made up of different silicate minerals. Nephrite jade consists of the calcium- and magnesium-rich amphibole mineral actinolite (aggregates of which also make up one form of asbestos). The rock called jadeitite consists almost entirely of jadeite, a sodium- and aluminium-rich pyroxene. The trade name Jadite is sometimes applied to translucent/opaque green glass.

The English word 'jade' is derived from the Spanish term piedra de ijada (first recorded in 1565) or 'loin stone', from its reputed efficacy in curing ailments of the loins and kidneys. 'Nephrite' is derived from lapis nephriticus, the Latin version of the Spanish piedra de ijada.

Nephrite and jadeite were used by people from the prehistoric for similar purposes. Both are about the same hardness as quartz, and they are exceptionally tough. They are beautifully coloured and can be delicately shaped. Thus it was not until the 19th century that a French mineralogist determined that "jade" was in fact two different materials.

Among the earliest known jade artifacts excavated from prehistoric sites are simple ornaments such as rounded beads, buttons, and tubular jades. Additionally, jade was used for axe heads, knives, and other weapons. As metal-working technologies became available, the beauty of jade made it valuable for ornaments and decorative objects. Jade has a Mohs hardness of between 6.5 and 7.0, so it can be worked with quartz or garnet sand, and polished with bamboo or even ground jade.

Nephrite can be found in a creamy white form (known in China as "mutton fat" jade) as well as in a variety of green colours, whereas jadeitite shows more colour variations, including dazzling blue, lavender-mauve, pink, and emerald-green colours. Of the two, jadeite is rarer, documented in fewer than 12 places worldwide.

Translucent emerald-green jadeitite is the most prized variety, both now and historically. As "quetzal" jade, bright green jadeitite from Guatemala was treasured by Mesoamerican cultures, and as "kingfisher" jade, vivid green rocks from Burma became the preferred stone of post-1800 Chinese imperial scholars and rulers. Burma (Myanmar) and Guatemala are the principal sources of modern gem jadeitite, and Canada of modern lapidary nephrite. Nephrite jade was used mostly in pre-1800 China as well as in New Zealand, the Pacific Coast and Atlantic Coasts of North America, Neolithic Europe, and south-east Asia. In addition to Mesoamerica, jadeitite was used by Neolithic Japanese and European cultures.

Jade is the official gemstone of British Columbia, where it is found in large deposits in the Lillooet and Cassiar regions. It is also the official gemstone of the state of Alaska, found particularly in the Kobuk area. A two ton block of jade sits outside the Anchorage Visitor’s Center in downtown Anchorage, Alaska, mined from near Kobuk and donated to the city as a showpiece.

Jade may be enhanced (sometimes called "stabilized"). There are three main methods, sometimes referred to as the ABC Treatment System:

• Type A: jadeite has not been treated in any way except surface waxing. This type of jadeite, carat by carat, is the most expensive gem in the world, even more so than diamond.
• Type B: treatment involves exposing a promising but stained piece of jadeite to chemical bleaches and/or acids and impregnating it with a clear polymer resin. This results in a significant improvement of transparency and colour of the material. Currently, infrared spectroscopy is the only test for the detection of polymer in jadeite.
• Type C: jade has been artificially stained or dyed. The red colour of Red jade can be enhanced with heat. The effects are somewhat uncontrollable and may result in a dull brown. In any case, translucency is usually lost.
  Type A treatment is the only enhancement acceptable to professional collectors.

Many minerals are sold as jade. Some of these are: serpentine (also bowenite), carnelian, aventurine quartz, glass, grossularite, Vesuvianite, soapstone (and other steatites such as shoushan stone) and recently, Australian chrysoprase. "Korean jade," "Suzhou jade," "Styrian jade," "Olive jade", and "New jade" are all really serpentine; "Transvaal jade" or "African jade" is grossularite; "Peace jade" is a mixture of serpentine, stichtite, and quartz; "Malaysia jade" is dyed quartz; "Mountain jade" is dyed dolomite marble.

In almost all dictionaries, the Chinese character 'yù' (?) is translated into English as 'jade'. However, this frequently leads to misunderstanding: Chinese, Koreans, and Westerners alike generally fail to appreciate that the cultural concept of 'jade' is considerably broader in China and Korea than in the West. A more accurate translation for this character on its own would be 'precious/ornamental rock'. It is seldom, if ever, used on its own to denote 'true' jade in Mandarin Chinese; for example, one would normally refer to 'ying yu' (??, 'hard jade') for jadeite, or 'ruan yu' (??, 'soft jade') for nephrite. The Chinese names for many ornamental non-jade rocks also incorporate the character 'yù', and it is widely understood by native speakers that such stones are not, in fact, true precious nephrite or jadeite. Even so, for commercial reasons, the names of such stones may well still be translated into English as 'jade', and this practice continues to confuse the unwary.

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