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The most important property of nephrite jade is its toughness, which explains its widespread use for axe heads, knife blades, and delicate, durable carvings. Toughness in this context is the opposite of brittleness, and is a quite different property to hardness, which is simply the resistance of a material to scratching.

So, toughness isn't hardness; toughness is opposite brittleness. Well, what exactly is toughness? Is it simply that it doesn't fall apart upon impact? You club somebody in the head with your jade club, and it stays in one piece, although another club of another material might have hit the person in the head with a harder wallop?

By the way, thanks, Stales.