What is Quartz?
Quartz is one of the most common and varied minerals on earth, and its abundant colors produce many gemstone types. Amethyst and Citrine are the most popular and valuable gem varieties of Quartz, but other forms also make important gemstones. Chalcedony describes any form of Quartz that is microcrystalline, in compact form without any visible crystals. Chalcedony also has several varieties used as gemstones, most notably Agate, Carnelian, Tiger's Eye, and Chrysoprase.
Pure Quartz, which is also known as Rock Crystal, is colorless. Various impurities are responsible for the extensive range of colors. The main crystalline Quartz varieties used as gemstones are described below.
Amethyst, the purple variety, is the most popular and valuable Quartz gemstone. Amethyst ranges from light to dark purple. See the Amethyst gemstone page for more details.
Citrine is the yellow, orange, or reddish-brown variety of Quartz. It is usually colored by heat treatment of Amethyst or Smoky Quartz. Light yellow or lemon yellow Citrine is often called Lemon Quartz in the gem trade. See the Citrine gemstone page for more details.
Smoky Quartz is the brown "smoky" variety of Quartz. It ranges in color from light brown to black. Despite its dark color, it is rarely opaque. See the Smoky Quartz gemstone page for more details.
The rosy pink variety of Quartz is known as Rose Quartz, and its color is usually soft, ranging from very light pink to medium pink in intensity. Rose Quartz is often milky or hazy, and it may lack good transparency. See the Rose Quartz gemstone page for more details.
The colorless, transparent variety of Quartz, free of any impurities, is known as "Rock Crystal". Flawless and very large cuts may be cut from Rock Crystal.
Milky Quartz is the white, translucent to opaque variety of Quartz. Though very common in nature, it is not used as a gemstone.
Colorless Quartz with golden yellow Rutile inclusions, as hairlike growths within the gemstone, are known as Rutilated Quartz. See the Rutilated Quartz gemstone page for more details.
Ametrine is an interesting, color-zoned combination of purple Amethyst and brownish-yellow Citrine. See the Ametrine gemstone page for more details.
Prasiolite, or Green Quartz, describes a light green Quartz artificially colored by heat treatment of certain types of Amethyst. May also be called "Green Amethyst" by some jewelers.
The blue variety of Quartz, which is uncommon in nature, is seldom used as a gemstone. Most "Blue Quartz" is clear Rock Crystal irradiated with gold to from a deep sky blue color. Blue Quartz may also refer to a dull grayish-blue Quartz in massive form with Crocidolite inclusions.
Colorless Quartz with Tourmaline inclusions, often as thin long black crystals, is known as "Tourmalinated Quartz".
Cat's Eye Quartz is Quartz with dense, tiny Rutile inclusions that cause a cat's eye effect. It is not common, and the chatoyant effect is usually weak. Cat's Eye Quartz is usually grayish in color and translucent.
All forms of Quartz are used as gemstones, and they are all affordable. They are cut into various gemstone cuts and cabochons, and used in all forms of jewelry. Lesser quality stones are often tumbled for use in bracelets, necklaces, and as costume jewelery. Large spheres and carvings are also cut from all the Quartz forms. Due to its abundance and lack of luster, Rock Crystal is not commonly cut into gemstones, although some very large spheres and sculptures are carved from it. Small crystals of Rock Crystal are sometime worn as pendants, sometimes being polished and smoothed, and sometimes in their entirely natural crystal form.
Varieties specific to Amethyst, Citrine, Smoky Quartz, Rose Quartz, Rutilated Quartz, and Chalcedony are listed separately.
Amethyst	- Purple variety of Quartz, and its most popular and valuable gemstone variety. (See the Amethyst gemstone page for more details.) Tumbled Amethyst with white Milky Quartz is sometimes known as Amethyst Quartz.
Aventurine	- Opaque, compact Quartz / Chalcedony containing small Mica, Hematite, or Goethite scales which cause a glistening effect. Aventurine is most often green but may also be other colors such as gray, orange, and brown.
Blue Quartz - Rare natural blue variety of Quartz. It is caused by inclusions of blue minerals, especially Dumortierite. Most "Blue Quartz" is what is popularly known as "Aqua Aura", essentially clear Rock Crystal synthetically irradiated with gold to form a deep sky blue color. Blue Quartz may also refer to a dull grayish-blue Quartz in massive form with Crocidolite inclusions.
Cat's Eye Quartz - Quartz with dense, tiny Rutile inclusions that cause a cat's eye effect. Cat's Eye Quartz is not common, and the chatoyant effect is usually weak. Cat's Eye Quartz is usually grayish in color and translucent.
Lemon Quartz - Lemon Quartz is a light to dark yellow Citrine, distinguished from most Citrine by lacking orange, brown, or reddish tints. More often though it is clear Quartz that is irradiated to produce an intensely colored yellow gemstone. Lemon Quartz has recently experienced a popularity increase in the gemstone market.
Milky Quartz - White, translucent to opaque variety of Quartz. It is not commonly used as a gemstone.
Prase - Light to emerald green, transparent to translucent Quartz / Chalcedony, with coloring caused from inclusions of green minerals, such as Actinolite, Hedenbergite, Chlorite, or Malachite.
Prasiolite - Light green gem form Quartz artificially colored by heat treatment of certain types of Amethyst. May also be called Green Amethyst by some jewelers.
Rock Crystal - The colorless, transparent variety of Quartz, free of impurities is called "Rock Crystal".
Tourmalinated Quartz - Quartz with splintery Tourmaline inclusions.
Amethyst may be heat treated to deepen the purple color. Most gem Citrine is produced by heat treating Amethyst, and the green Quartz known as Prasiolite or "Green Amethyst" is also produced by heating Amethyst from specific localities.
Certain colorful Quartz types not found in nature are produced through irradiation. Some forms of Quartz with a multicolored rainbow effect are synthetically treated to produce their color effect using film deposition. The process involves bonding an extremely thin metallic film layer over the top of the gemstone, so that the interesting color effects are reflected from the crown. Some vividly colorful forms of Quartz are synthetic grown using the hydrothermal method.
Quartz is extremely common and is found in numerous localities throughout the world. The important sources are far too numerous to mention, though in general the most prolific countries that produce Quartz gemstones are Brazil, Madagascar, India, and the U.S. (Arkansas). Specific sources for the popular Quartz varieties are described on their dedicated pages.
See the individual variety pages for specific variety similarities.
Rock crystal is similar to glass, but the softness of glass usually lends it to scratches and soft etches which are lacking on Rock Crystal. Rock Crystal is rarely cut into small facets, so it usually is not a concern of confusion to other colorless gems such as Diamond, White Topaz, and White Sapphire. These white gemstones will also have a greater dispersion and exhibit more fire.
Additional images for the varieties Amethyst, Citrine, Smoky Quartz, Rose Quartz, Rutilated Quartz, and Chalcedony are listed separately.
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