Quartz is the most common of all minerals and is found in many different rocks and ore deposits. There are many varieties of quartz. Amethyst, citrine, aventurine, rose quartz and smoky quartz are part of the quartz family. Quartz crystals generates an electrical charge and is useful and most importantly used in the fields of radio, television, and radar. It is also used in making sandpaper and grindstones. Quartz sands are used in the manufacture of glass and mortar. Hardness: Hard (7) Glassy or waxy luster