  Levitated systems in vacuum have many potential applications ranging from new
types of inertial and magnetic sensors through to fundamental issues in quantum
science, the generation of massive Schrodinger cats, and the connections
between gravity and quantum physics. In this work, we demonstrate the passive,
diamagnetic levitation of a centimeter-sized massive oscillator which is
fabricated using a novel method that ensures that the material, though highly
diamagnetic, is an electrical insulator. By chemically coating a powder of
microscopic graphite beads with silica and embedding the coated powder in
high-vacuum compatible wax, we form a centimeter-sized thin square plate which
magnetically levitates over a checkerboard magnet array. The insulating coating
reduces eddy damping by almost an order of magnitude compared to uncoated
graphite with the same particle size. These plates exhibit a different
equilibrium orientation to pyrolytic graphite due to their isotropic magnetic
susceptibility. We measure the motional quality factor to be Q~1.58*10^5 for an
approximately centimeter-sized composite resonator with a mean particle size of
12 microns. Further, we apply delayed feedback to cool the vertical motion of
frequency ~19 Hz from room temperature to 320 millikelvin.
