= Solution
<Diamond> can be \b[metastable]: its <Gibbs free energy> is higher than <graphite>'s under ambient conditions, but transformation is kinetically inhibited. Conversion requires substantial rearrangement of the strong carbon-bond network and the formation and growth of a new <thermodynamic phase>, with an activation and <nucleation barrier>.
At room temperature the rate can be extremely small even though the free-energy change favors <graphite>. Thermodynamic stability specifies the preferred equilibrium state, not the time needed to reach it. Persistence of <diamond> therefore does not contradict <graphite>'s ambient equilibrium stability.
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