Fused Quartz is produced by melting naturally occurring quartz crystal at high temperatures, while Synthetic Quartz Glass is manufactured using a chemical process. This process, called the hydrothermal process, involves dissolving Silicon Dioxide in water at high pressure and then re-depositing it at a lower pressure to form quartz. Synthetic Quartz Glass is generally purer than Fused Quartz and is often used in applications requiring high purity, like the semiconductor industry or precision optics.