We report on high-quality microcrystalline diamond films deposited on Si substrates in microwave hydrogen plasma (without methane feed gas) using graphite powders with different sizes from 2 mu m to 150 mu m as the carbon source. Hydrocarbon radicals, necessary for diamond growth, are produced in course of the graphite etching by atomic hydrogen, and supplied into the plasma for further participation in diamond formation on the substrate. Owing to the large open surface area of the powder the approach allows a continuous long-term stable flux of hydrocarbons (as determined via in situ optical emission spectroscopy of the plasma) during the 10 h graphite etching process. The produced diamond films with grain size of similar to 1 mu m were characterized with scanning electron microscopy and Raman spectroscopy, and exhibited similar morphology and crystallinity independent on the graphite powder dimensions.