Final answer:
Cleaving is not a method that produces synthetic gemstones; it is used to cut or split a gemstone based on its natural crystal structure. The other processes mentioned are all used to create synthetic gemstones.
Step-by-step explanation:
The process that will NOT produce a synthetic gemstone is d) Cleaving. Cleaving is the process of cutting or splitting a diamond or gemstone along its natural crystal structure. It is a method used in the gemstone cutting industry to shape and size diamonds and other gemstones, not to create synthetic versions.
The other processes listed, such as Flame Fusion, the Czochralski Process, and Hydrothermal Growth, are all methods used to produce synthetic gemstones. These procedures emulate the conditions necessary to grow crystals that are chemically, physically, and optically similar to natural gemstones.