  Data from the MINOS experiment has been used to search for mixing between
muon neutrinos and muon antineutrinos using a time-independent
Lorentz-violating formalism derived from the Standard-Model Extension (SME).
MINOS is uniquely capable of searching for muon neutrino-antineutrino mixing
given its long baseline and ability to distinguish between neutrinos and
antineutrinos on an event-by-event basis. Neutrino and antineutrino
interactions were observed in the MINOS Near and Far Detectors from an exposure
of 10.56$\times10^{20}$ protons-on-target from the NuMI neutrino-optimized
beam. No evidence was found for such transitions and new, highly stringent
limits were placed on the SME coefficients governing them. We place the first
limits on the SME parameters $(c_{L})^{TT}_{\mu\mu} $ and
$(c_{L})^{TT}_{\tau\tau}$ at $-8.4\times10^{-23} < (c_{L})^{TT}_{\mu\mu} <
8.0\times10^{-23}$ and $-8.0\times10^{-23} < (c_{L})^{TT}_{\tau\tau} <
8.4\times10^{-23}$, and the world's best limits on the
$\tilde{g}^{ZT}_{\mu\overline{\mu}}$ and $\tilde{g}^{ZT}_{\tau\overline{\tau}}$
parameters at $|\tilde{g}^{ZT}_{\mu\overline{\mu}}| < 3.3\times 10^{-23}$ and
$|\tilde{g}^{ZT}_{\tau\overline{\tau}}| < 3.3\times 10^{-23}$, all limits
quoted at $3\sigma$.
