Due to the value and demand of the gem varieties of corundum (ruby, sapphire) as well as beryl (emerald, aquamarine), diamond and quartz (amethyst, citrine), an increasing number of synthetic stones of these gem varieties is produced. With improving techniques it is easy for synthetic gems to grow with properties similar to those of their natural counterparts or even stones without significant inclusions of diagnostic value. For this reason, the determination of physical properties of gems, using techniques such as infrared spectrometry, laser Raman microprobe spectrometry, fluid inclusions, solid inclusions, cathodoluminescence, luminescence and fluorescence, is becoming increasingly important as additional and easily perfomable methods for the distinction of natural and synthetic gemstones.