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Quartz Mineral Facts:

Chemical Formula: SiO₂  The Mineral is 46.7% Silicon by weight.
The mineral is pyroelectric and circularly polarizing. It is an electric insulator at ordinary temperatures.

Colors: Pure specimens are transparent or colorless, but most varieties are colored by the addition of pigments or impurities. When the coloring matter is opaque it may be present in sufficient quantity to render the mineral also opaque.

Hardness: 7

Density: 2.65

Cleavage: None  

Crystallography: Hexagonal
Hexagonal-rhombohedral; trapezohedral. Commonly found in the form of crystals. Crystals commonly prismatic, with prism faces horizontally striated. Crystals at times very much distorted, when the recognition of the prism faces by their horizontal striations will assist in the orientation of the crystal. From large crystals usually attached at one end, to finely crystalline coatings, forming "drusy" surfaces. Also common in massive forms of great variety. From coarse- to fine-grained crystalline to flint like or cryptocrystalline varieties.

Luster:. Its luster is vitreous, or sometimes greasy.

Optics: (Refractive Index):  a = 1.730; b = 1.758; y = 1.838

Quartz Crystals 

Composition, Structure and Associated Minerals:
Silicon and Oxygen are the two most common elements in the earths crust, and the combination of them forms quartz. The mineral quartz occurs as an essential constituent of many crystalline rocks such as granite, gneiss, etc., and as the almost sole component of certain sandstones. It constitutes the greater portion of most sands and the material of many veins. It also occurs as pseudomorphs after shells and other organic bodies embedded in rocks, having replaced the original substance of which these bodies were composed. It is also one of the decomposition products of many silicates. It may thus be primary or secondary in origin. It may result from igneous or aqueous processes, or it may be a sublimation product.

Quartz resists most of the chemical agents except the alkalies. It dissolves in fused sodium carbonate and in solutions of the caustic alkalies. It is also soluble in HF and to a very slight degree in water, especially in water containing small quantities of certain salts. When heated to 575 the alpha variety passes into the Beta variety; at 870 both varieties pass into tridymite, and at 1470 the tridymite passes over into cristobalite. Gradual fusion occurs just below 1470. The varieties of quartz have received many different names depending largely upon their color and the uses to which they are put. They may be grouped for convenience into crystallized and crystalline varieties. The principal crystallized varieties are:

Above: Amethyst Purple quartz.

Identification and Diagnostics
Infusible an insoluble. Quartz yields a clear glass when the finely powdered mineral is fused with an equal volume of sodium carbonate. Usually identified by its glassy luster, conchoidal fracture, hardness of 7 and crystal form.

Uses:
Quartz is widely used in its various colored forms as gem and ornamental material, as amethyst, rose quartz, cairngorm, cat's-eye, tiger's eye, aventurine, carnelian, agate, onyx, etc. Used for abrading purposes either as quartz sand or as sandpaper. Used in the manufacture of porcelain, of glass, as a wood filler, in paints, scouring soaps, etc. As sand is used in mortars and cements. Large amounts of quartz sand are used as an acid flux in certain smelting operations.

Its most extensive use, however, is in the manufacture of glass and pottery. Earthenware, porcelain and some other varieties of potter's ware are vitrified mixtures of clay and ground quartz, technically known as "flint." Ordinary glass is a silicate of calcium or lead and the alkalies, sodium or potash. It is made by melting together soda, potash, lime or lead oxide and ground quartz or quartz sand, and coloring with some metallic salt. A pure quartz glass is now being made for chemical uses by melting pure quartz sand.

In the form of sandstone, it is used as a building stone, for paving purposes, etc.  In the form of sand it is employed in various building operations. Bricks cut from dense quartzites (very hard and compact sandstones) are often employed for lining furnaces. The uses of honestones, oilstones, and whetstones are indicated by their names.

Above: Gold in vein quartz, mother lode.

Occurrence, Localities and Origins:
Quartz is the most common of minerals. It occurs as an important constituent of the acid igneous rocks, such as granite, rhyolite, pegmatite, etc. It is a common mineral of sedimentary rocks, forming the chief mineral in sandstone. It occurs largely also in metamorphic rocks, as gneisses and schists, while it forms practically the only mineral of quartzites. Deposited often from solution and forms the most common vein and gangue mineral. In rocks it is associated chiefly with feldspar and muscovite; in veins with practically the entire range of vein minerals. Often carries gold and becomes an important ore of that metal. Occurs in large amount as sand in stream beds and upon the seashore and as a constituent of soils.

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Japan Law quartz crystal Twin

Vein quartz, Mariposa County, California
 

Rose quartz, South Dakota, USA

Petrified (Fossilized) Wood, Jasper quartz, Arizona

Amethyst-Citrine quartz, known as Ametrine

Above: Fire Agate (Cryptocrystaline quartz), Arizona

Nevada Outback Gems