Precursors for zircon-carbon mixtures were made to coat fibers for ceramic-matrix composites. Precursors were characterized using XRD, TGA, and DTA. Zircon formed from vanadium- or lithium-doped precursors after heat treatments at greater than or equal to900degreesC in air, but it did not form at 1200degrees-1400degreesC in argon when large amounts of carbon were added. Some precursors were used to coat Nextel(TM)720 and Hi-Nicalon(TM) fibers. The coatings were characterized using SEM and TEM, and coated-fiber tensile strengths were measured. Although zircon formed in powders, only tetragonal-zirconia-silica mixed phases formed in fiber coatings at 1200degreesC in air. Loss of vanadium oxide flux to the fibers may have caused the lack of conversion to zircon. The strengths of the coated fibers were severely degraded after heat treatment at greater than or equal to1000degreesC in air, but not in argon. The coated fibers were compared with zirconia-carbon-coated fibers made using similar methods. Mechanisms for fiber strength degradation are discussed.