Pure quartz and gemstone amethyst are different varieties of quartz. Quartz is a chemical compound made up of silicon and oxygen. As both pure quartz and gemstone amethyst are quartz, these have the same chemical properties.
Pure quartz is also known as rock crystal or clear crystal. It is transparent and colorless. Gemstone quartz is a quartz of purple color. Thus the physical property that differentiates a pure quartz from amethyst is the color of the compound.
