An ornamental stone, jade is a name applied to two related minerals, the nephrite form of actinolite (a mineral that also includes a form of asbestos), and a mineral called jadeite. The former is a calcium magnesium iron silicate hydroxide, with the formula Ca2(Mg, Fe)5Si8O22(OH)2, and the latter is a sodium aluminum silicate, with the formula NaAlSi2O6. The two are closely related, and it wasn't until 1863 that people could distinguish between the two forms of this stone.
It is an exceptionally tough material, and was first used for things such as axe heads, knives, and weapons. Later, as other materials could replace jade as a weapons material, it became appreciated for its beauty.
Nephrite can be found in a creamy white form as well as a green color, while jadeite shows more color variation. Of the two, jadeite is rarer, and is the form of jade mostly used in Central America. Nephrite jade was used mostly in China.
In New Zealand, where it is known as greenstone, jade was fashioned for centuries by Maori to make weapons and ornaments, and is still widely used to make souvenirs although the mining of it is restricted and closely monitored.