Purple Quartz
Ranging from lavender to deep shades of purple, amethyst is quartz crystal that has an impurity of iron. It is the most valuable of the colorful quartz varieties and is widely used in jewelry and decorative designs. High quality amethyst is very dark and often features unevenly distributed color stratification, which gives it flashes of red when held up to the light. Amethyst is found abundantly in many parts of the world and was believed by many cultures to have protective energies and powers. Other types of purple quartz crystals include ametrine, which is found only in South America.
Yellow Quartz
Tigers eye and citrine are the most comon forms of yellow quartz, the difference being that citrine is clear while tigers eye is opaque. The yellow hue in citrine is caused by an iron impurity and can be made from amethyst by heating to stone to high temperatures (over 550 degree centrigrade). Tigers eye contains chalcedony, fibrous materials that cause the quartz to haved a striped appearance. Both tigers eye and citrine are often used for jewelry and are usually polished smooth.
Pink and Red Quartz
Carnelian and sard are solid but translucent quartz crystals that contain chalcedony fibers of red to brown hues. Rosy quartz contains rutile crystal, which gives it its particular hue and makes it somewhat smoky. These pink and red quartz crystals also have been used as decorative items in jewelry and are believed to possess protective powers by new-age practitioners.
Multi-colored quartz
Several varieties of quartz crystal contain multiple mineral impurities and sport several different colors at once. Bloodstone contains green chalcedony fibers as well as red iron oxide that give it the appearance of having veins of blood running through it. Jasper is a type of granulated quartz crystal that often contains red, yellow and brown, and is known for its unique spotted patterns, many of which make up abstract shapes when the stone is polished. Agate contains bands of various colors that are usually light and translucent, and form a beautiful spectrum when held up to the light.