Powder x-ray diffraction (XRD) and Raman evidence are presented for the formation of crystalline diamond in the “hydrothermal” pressure-temperature regime 1–5 kbars, <1000 °C. Two different methods appear to enable diamond to nucleate and grow. One—a Low Pressure Solid-State Source (LPSSS) route—utilizes special solid precursors, especially low temperature glassy carbon (GC-500), with very fine diamond seeds in sealed gold capsules with H2O at, say, 800 °C and 1 kbar. The other includes pyrolysis of highly selected organic solid/liquid precursors (halogenated aliphatics such as iodoform) onto similar diamond seeds. In all the cases, powder x-ray diffraction evidence shows a marked increase of the diamond XRD peaks, likewise the Raman spectrum shows a strong increase of the 1331 cm−1 line. However, the crystals apparently are too small to be seen in the SEM. TEM diffraction data, on the other hand, seem to lend support to the possibility of all the grown diamonds being very small.