superhard
... that diamond is superhard but not supertough?
... that <a href="./Diamond" id="mwBEg" rel="mw:WikiLink" title="Diamond">diamond</a> <i id="mwBEk">(example pictured)</i> is <b id="mwBEo"><a class="mw-redirect" href="./Superhard_materials" id="mwBEs" rel="mw:WikiLink" title="Superhard materials">superhard</a></b> but not <a href="./Fracture_toughness" id="mwBEw" rel="mw:WikiLink" title="Fracture toughness">supertough</a>?