  We evaluate static properties and semileptonic decays for the ground state of
doubly heavy $\Xi, \Xi', \Xi^*$ and $\Omega, \Omega', \Omega^*$ baryons.
Working in the framework of a nonrelativistic quark model, we solve the
three--body problem by means of a variational ansazt made possible by heavy
quark spin symmetry constraints. To check the dependence of our results on the
inter-quark interaction we use five different quark-quark potentials that
include a confining term plus Coulomb and hyperfine terms coming from
one--gluon exchange. Our results for static properties (masses, charge and mass
radii, magnetic moments...) are, with a few exceptions for the magnetic
moments, in good agreement with a previous Faddeev calculation. Our much
simpler wave functions are used to evaluate semileptonic decays of doubly heavy
$\Xi,\Xi'(J=1/2)$ and $\Omega, \Omega'(J=1/2)$ baryons. Our results for the
decay widths are in good agreement with calculations done within a relativistic
quark model in the quark--diquark approximation.
