Types of quartz crystals

Being available and versatile, quartz crystals can be easily found and used for a variety of purposes. Many commonly used crystals fall under the quartz family. Each different type possesses different qualities and associations.
Amethyst   
One of the most popular types of quartz crystals is amethyst. Amethysts are translucent purple stones that range from lightly tinted to deep hues. The color purple is generally associated with spirituality and the mind. Wearing or carrying an amethyst helps with clarity of thought for mental activities or helps improve psychic abilities. They are beneficial when used during meditation to stimulate prophetic dreams, or when practicing divination, such as tarot card readings.
Onyx
Black is the color of grounding and protection, so black onyx is ideal for any workings involving these energies. Wear black onyx jewelry for general protection and to repel negative energy. Black onyx also has the ability to absorb unwanted energy from your body, just the way any black object would absorb heat if left out in the sun.
Tiger's-Eye
Tiger's-eye is a banded crystal that is most commonly brown, but there are also blue and green tiger's-eye. The stone is associated with the element of earth, which rules over things physical and material: strength, stability and abundance. It can be carried or worn to increase personal power, or to help you gain control of yourself and ground or center your energy. It is also commonly used to promote prosperity and draw wealth to the user. People who need discipline can benefit from keeping a tiger's eye on them.
Rock Quartz
Clear rock quartz, the most versatile of all crystals, is something of an all-purpose crystal. It can replace any crystal that you happen to lack and be charged with whatever purposes you desire, or it can be used in combination with other crystals to increase their power. They can be used to balance and amplify energy, so you can place other types of crystals and stones upon a piece of quartz to charge them. Blue quartz is ideal for peace and healing. Rose (pink) quartz is used in matters of love, friendship and romance. Smoky quartz, which is clouded with gray or brown, is good for grounding. Milky quartz, clouded with white, is good for stress reduction and calming.
Because of the diversify and suitability, the quartz crystals are often used to make the jewelry. And people adore them also owing to their connotative meaning and healing ability.