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Chemical Formula | SiO2 | |
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Composition | Silicon dioxide | |
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Color | Occurs in an infinite range of colors. Most commonly white, purple, brown, and colorless. Many specimens are multicolored or banded. | |
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Streak | White | |
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Hardness | 7 | |
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Crystal Forms and Aggregates |
(Hexagonal) The crystal structure of Quartz
is a complicated topic, and one must go into considerable
detail to fully analyze this subject. (Brief explanation on the crystal structure of Quartz) Quartz forms unusual crystals. As a result of a changeover from alpha to beta Quartz, crystals form as hexagonal prisms with their termination pyramids modified by rhombohedral faces. The crystals are commonly large, single, and faultless. They are usually prismatic, but often stubby. These crystals may also be in disorganized aggregates. Crystals are usually striated horizontally, and are sometimes doubly terminated. Crystal habits include: drusy, grainy, in geodes, bladed, rounded waterworn pebbles, radiating, pointy pyramids on a matrix, dense agglomerations of small crystals, massive, globular, stalactitic, crusty, and in nodules. Crystals frequently twin; a famous twinning habit is the Japanese twin, where two crystals contact at a 90º angle. Quartz crystals may also contain certain "growths". One is a scepter growth, where the top of a crystal bulges out from the rest of the crystal, and another is a phantom growth, where one crystal forms over another, leaving a ghosted form inside. |
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Transparency | Transparent to opaque | |
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Specific Gravity | 2.6 - 2.7 | |
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Luster | Most specimens have a vitreous luster. Some yellow or brown varieties have a resinous luster, and earthy specimens are dull in luster. Transparent, colorless Quartz crystals from a few distinct localities have an adamantine luster. | |
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Cleavage | Indiscernible. Seldom exhibits parting. | |
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Fracture | Conchoidal | |
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Tenacity | Brittle | |
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Other ID Marks | 1) Many specimens fluoresce, mainly white and green 2) All specimens are triboluminescent 3) All specimens are piezoelectric |
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Other Names |  Silica (describes Quartz,
Chalcedony, and Opal) Crystalline
Quartz or Macrocrystalline Quartz
(distinguishes Quartz from Chalcedony, or Microcrystalline Quartz) Alpha
Quartz or High Quartz
(describes Quartz stable at normal room conditions.(More information about the crystal structure of Quartz) |
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Varieties | There are literally hundreds of different
names given to Quartz and Chalcedony. Some are not scientifically recognized,
but are used universally. The most important names are
listed below; all other names are listed in an individual
page of Quartz and Chalcedony varieties. (Quartz and Chalcedony variety page) These are the main varieties:  Chalcedony- Microcrystalline variety Amethyst - Purple variety Citrine - Yellow to yellow-brown variety Rose
Quartz -
Pink varietyRock Crystal - Colorless, transparent variety Smoky Quartz - Brownish-black, "smoky" variety Milky Quartz - White, translucent to opaque variety Rutilated Quartz - Quartz with golden-yellow, needlelike Rutile inclusions Aventurine - Opaque, massive Quartz containing small mica, Hematite, or Goethite scales which cause a glistening effect. |
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Polymorphs | See Polymorphs of SiO2 See also: Chalcedony Opal Melanophlogite |
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In Group | Silicates ; Tectosilicates ; Silica group May be classified as an oxide by a few abstract references (Oxides ; Simple oxides) |
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All About | The complexity involved in this one mineral
is so great that entire books just about Quartz have been
written. The information provided here just briefly
touches upon all the details of this mineral. Quartz is the most common mineral on earth (second most common if Water is considered a mineral). It occurs in basically all mineral environments, and is an important constituent of many rocks. Quartz is also the most varied of all minerals. It occurs in all different forms, habits, and colors. There are more variety names given to Quartz than any other mineral. The mineral Chalcedony, is, in essence, a variety of Quartz. It is also known as Microcrystalline Quartz, for it is a form of Quartz that only occurs in microscopic, compacted crystals. However, most mineral references list Quartz and Chalcedony as two separate minerals. This page deals only with crystalline (form in visible crystals) Quartz. Chalcedony has its own page in this guide. There are light blue, transparent Quartz crystals in the market. They are not naturally colored, but Rock Crystal (transparent colorless Quartz crystals) synthetically tinted with irradiation of gold. A few dealers sell them as "Blue Rock Crystal", without informing the buyer that these crystals are not naturally colored. In some localities, Hematite forms an incrustation pseudomorph over Quartz crystals. This causes a crystal to become opaque and reddish brown, and occasionally gives the crystal a multicolored, iridescent effect. Quartz frequently forms the inner lining of geodes. The geodes may contain large crystals, or may be of globular, microcrystalline Quartz. (More information on Quartz Geodes) |
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Uses | Quartz is an important mineral with numerous
uses. Sand, which is composed of tiny Quartz pebbles, is
the primary ingredient for the manufacture of glass.
Transparent Rock Crystal has many electronic
uses; it is used as oscillators in radios, watches, and
pressure gauges. Quartz is also used as an abrasive for sandblasting, grinding glass, and
cutting soft stones. Quartz is important in the production of soaps and ceramics. Transparent Rock Crystal is used in the study of optics. Quartz is essential in the computer industry, for the all-important silicon semiconductors are made from Quartz. Beside for all these practical uses, Quartz is important in the gem trade. Many varieties are faceted as gems, and some are well known. Amethyst is the most popular Quartz gem, and Citrine is the most valuable. Rose Quartz, Smoky Quartz, Rock Crystal, and Aventurine are also cut into gems. Clear Quartz crystals are worn by some as pendants for good luck. Quartz specimens are also very popular among collectors. Certain collectors specialize their entire collection on different types of Quartz. |
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Striking Features | Hardness, crystal forms, striations on crystal faces, and frequent appearance of conchoidal fractures on crystal faces. | |
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Complex Tests | Dissolves in hydrofluoric acid | |
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Popularity (1-4) | 1 | |
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Prevalence (1-3) | 1 | |
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Demand (1-3) | 1 | |
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Distinguishing Similar Minerals |
Beryl - harder (7½ - 8), lacks
horizontal striations Feldspars - Softer (6), perfect cleavage Calcite - Much, much softer (3) |
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Commonly Occurs With |
Quartz occurs in virtually all mineral environments, and may be associated with almost every mineral. | |
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Noteworthy Localities |
(Amethyst localities are mentioned on the
Amethyst page) (Citrine localities are mentioned on the Citrine page) Fine Quartz specimens can be obtained from numerous localities; only a select few are mentioned here. Large, flawless Rock Crystal of exceptional quality comes from Hot Springs, Garland Co. Arkansas and Mount Ida in the Ouachita Mountains, Montgomery Co., Arkansas. Excellent crystals of the same type also come from Dauphine, France; Ambatofinandrahana, Madagascar; and Minas Gerais, Brazil. Enormous pieces of transparent Rock Crystal were found at Mokelumne Hill, Calaveras Co., California. Brilliant, doubly terminated crystals come from Middleville and Little Falls, Herkimer Co., New York, where they are known as "Herkimer Diamonds". It is a scientific oddity why Rose Quartz so infrequently forms crystals. Almost all Rose Quartz is massive, and fine crystals are quite rare. Crystals are occasionally found in the Petora mine, Minas Gerais, Brazil, and Newry and Paris, Maine. A few crystals were also reported in Pala, San Diego Co., California. Deeply colored, massive Rose Quartz is found in numerous localities in Minas Gerais, Brazil, and the best American material of this sort is from the Black Hills of South Dakota (near Custer, Custer Co.). Fine Smoky Quartz comes from the Pikes Peak area, El Paso Co., Colorado; Montgomery Co., Arkansas; Greenhorn Mountain, Kern Co., California; and in Switzerland in St. Gotthard, Ticino. Rutilated Quartz, occasionally crystallized, is found in the Ural Mountains of Russia and in Minas Gerais, Brazil. Odd crystals with green opaque bottoms (from Chlorite inclusions), and clear transparent tops are found in Saratoga Co., New York. |
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