Why do glass pebbles bounce when they hit a hard surface instead of breaking?
Both the above answers are correct. For a material to be weak the molecular bonds have to be naturally weak or weakened in some way. Extruding and forming glass into fine objects creates stresses that weaken the glass. Glass objects that are formed in a mould or freeformed and allowed to cool uniformly, are denser and less prone to failure. What makes the pebble so strong is a combination of the material itself and the way the pebble is formed. Of course the pebble doesn’t always come away unscathed, the surface (which cooled first) will often delaminate and crack away.
