With the exception of Hg, all metals are solid at 298 K; the
statement ‘solid at room temperature’ is ambiguous because
the low melting points of Cs (301 K) and Ga (303 K) mean
that in some countries, these metals are liquids. Table 5.2
shows that most metals crystallize with ccp, hcp or bcc
lattices. However, many metals are polymorphic and exhibit
more than one structure depending upon the conditions of
temperature and/or pressure; we return to this later.