Nanostructured diamond was grown by microwave plasma chemical vapour deposition onto 2 mm diameter quartz spheres using a H2/CH 4/N2 feedgas mixture high in methane concentration (15% by volume). Deposition experiments were performed at low temperature (<425°C, below the temperature limit of the optical pyrometer used) as well as at high temperature (830°C). Nucleation and growth of nanostructured diamond was found to occur readily in both cases. In addition, it was found that pre-treatment scratching is not necessary for achieving high diamond nucleation/growth rates on quartz, although scratching did result in a more uniform and smooth surface morphology, especially for low temperature deposition. All films grown at low temperature resulted in higher diamond quality with less amorphous carbon and non-diamond components. Plasma reduction of the exposed silica surface to create oxygen-containing species near the substrate surface may explain the improved diamond quality and practical nucleation/growth rates at such low temperature. © 2005 IOP Publishing Ltd.