Jade: nephrite and jadeite are two different minerals

Jade is not one mineral but a name applied to two chemically distinct ones, jadeite and nephrite. Jadeite is generally the more prized in fine jewelry, particularly the vivid green imperial jade material, and it has a slightly higher hardness and density than nephrite. Nephrite is tougher in the mechanical sense, meaning it resists breaking under impact extremely well, which is exactly why it was historically favored for tools and weapons in cultures without access to metal. Both are extremely fine grained and interlocking in structure at a microscopic level, which is what gives genuine jade its notable resistance to chipping compared to many other ornamental stones of similar hardness.