  One of the most important questions regarding the progenitor systems of Type
Ia supernovae (SNe Ia) is whether mergers of two white dwarfs can lead to
explosions that reproduce observations of normal events. Here we present a
fully three-dimensional simulation of a violent merger of two carbon-oxygen
white dwarfs with masses of $0.9 \mathrm{M_\odot}$ and $1.1 \mathrm{M_\odot}$
combining very high resolution and exact initial conditions. A well-tested
combination of codes is used to study the system. We start with the dynamical
inspiral phase and follow the subsequent thermonuclear explosion under the
plausible assumption that a detonation forms in the process of merging. We then
perform detailed nucleosynthesis calculations and radiative transfer
simulations to predict synthetic observables from the homologously expanding
supernova ejecta. We find that synthetic color lightcurves of our merger, which
produces about $0.62 \mathrm{M_\odot}$ of $^{56}\mathrm{Ni}$, show good
agreement with those observed for normal SNe Ia in all wave bands from U to K.
Line velocities in synthetic spectra around maximum light also agree well with
observations. We conclude, that violent mergers of massive white dwarfs can
closely resemble normal SNe Ia. Therefore, depending on the number of such
massive systems available these mergers may contribute at least a small
fraction to the observed population of normal SNe Ia.
