Jade is a semi-precious gemstone that has been prized since the Neolithic Age. Ancient cultures carved figurines and ritual objects from jade. The term "jade" is used for two different kinds of minerals which vary in color from pale green to dark green. Nephrite is a calcium silicate with varying amounts of magnesium and iron [Ca2(Mg,Fe)5Si8O22(OH)2]. The higher the iron content the greener the color. Jadeite is a sodium-aluminium silicate [NaAlSi2O6] with an interlocking crystal matrix. Jadeite has about the same hardness as quartz, while nephrite is somewhat softer.