STUblack holes and string triality

We find double-extreme black holes associated with the special geometry of the Calabi-Yau moduli space with the prepotential $F=STU$. The area formula is $\mathrm{STU}$-moduli independent and has ${\left[\mathrm{S}\mathrm{L}\right(2,\mathbf{Z}\left)\right]}^3$ symmetry in space of charges. The dual version of this theory without a prepotential treats the dilaton $S$ asymmetric vs $T$, $U$ moduli. We display the dual relation between new ($\mathrm{STU}$) black holes and stringy ($S|TU$) black holes using a particular Sp(8,Z) transformation. The area formula of one theory equals that of the dual theory when expressed in terms of dual charges. We analyze the relation between ($\mathrm{STU}$) black holes to string triality of black holes: ($S|TU$), ($T|US$), ($U|ST$) solutions. In the democratic $\mathrm{STU}$-symmetric version we find that all three $S$, $T$, and $U$ duality symmetries are nonperturbative and mix electric and magnetic charges.