Jade is a name shared by two distinctly different minerals-Nephrite, a calcium magnesium silicate, and Jadeite, a sodium aluminium silicate. Nephrite has a hardness of 6 and Jadeite has a hardness of 6.5 to 7. Both have monoclinic crystal systems and are exceptionally tough stones, a trait caused by their finely interlocked and strongly bonded crystal structures. The name Jade is derived, rather accidentally, from the Spanish term piedra de yjada (or lapis nephrictus in Latin), meaning ‘stone of the lion’. When the term was misprinted in a French translation, it became pierre le jade.