Upon hearing that ice is one of the few solids that is lighter than it’s liquid form, I wondered if God made the rule “All solids are heavier”. But then - the first winter happened, the ice sank to the bottom of the lakes and killed all the plant-life off.
“Oops - okay, everything except for water - solids will be heavier.”
Apart from water arsenic, bismuth, gallium, germanium and silicon all have higher density in liquid phase, i.e. the solid floats.