The name quartz is an old German word of uncertain origin first used by Georgius Agricola in 1530.
The name Silicium is derived from silica > Latin silex for flint (SiO 2), a hard stone. The Latin name silicium was adopted to conform with the -ium ending of most elements. The suffix -on in English was added because of its resemblance to Carbon.
English: Silica, Silicic anhydride, Silicon dioxid
German: Kieselsäure, Siliciumdioxid, Bergkristall
Minerals; Inorganic; Column Four
Hahnemann introduced it in Homoeopathic Materia Medica. Allen's Encyclop. Mat. Med. Vol. IX, 1.
Description of the substance
A white amorphous powder; tasteless and odourless. It is insoluble in water and in dilute acids, excepting only hydrofluoric acid.
Widely distributed mineral of many varieties that consists primarily of silica, or silicon dioxide (SiO2). Minor impurities such as lithium, sodium, potassium, and titanium may be present. Quartz has attracted attention from the earliest times; water-clear crystals were known to the ancient Greeks as krystallos-hence the name crystal, or more commonly rock crystal, applied to this variety.
Quartz is the second most abundant mineral in the Earth's crust after feldspar. It occurs in nearly all acid igneous, metamorphic, and sedimentary rocks. It is an essential mineral in such silica-rich felsic rocks as granites, granodiorites, and rhyolites. It is highly resistant to weathering and tends to concentrate in sandstones and other detrital rocks. Secondary quartz serves as a cement in sedimentary rocks of this kind, forming overgrowths on detrital grains. Microcrystalline varieties of silica known as chert, flint, agate, and jasper consist of a fine network of quartz.
Metamorphism of quartz-bearing igneous and sedimentary rocks typically increases the amount of quartz and its grain size.
Quartz exists in two forms: (1) alpha-, or low, quartz, which is stable up to 573° C (1,063° F), and (2) beta-, or high, quartz, stable above 573° C.
The two are closely related, with only small movements of their constituent atoms during the alpha-beta transition. The structure of beta-quartz is hexagonal, with either a left- or right-handed symmetry group equally populated in crystals. The structure of alpha-quartz is trigonal, again with either a right- or left-handed symmetry group. At the transition temperature the tetrahedral framework of beta-quartz twists, resulting in the symmetry of alpha-quartz; atoms move from special space group positions to more general positions. At temperatures above 867° C (1,593° F), beta-quartz changes into tridymite, but the transformation is very slow because bond breaking takes place to form a more open structure. At very high pressures alpha-quartz transforms into coesite (q.v.) and at still higher pressures, stishovite (q.v.). Such phases have been observed in impact craters.
Quartz is piezoelectric: a crystal develops positive and negative charges on alternate prism edges when it is subjected to pressure or tension. The charges are proportional to the change in pressure. Because of its piezoelectric property, a quartz plate can be used as a pressure gauge, as in depth-sounding apparatus.
Just as compression and tension produce opposite charges, the converse effect is that alternating opposite charges will cause alternating expansion and contraction. A section cut from a quartz crystal with definite orientation and dimensions has a natural frequency of this expansion and contraction (i.e., vibration) that is very high, measured in millions of vibrations per second. Properly cut plates of quartz are used for frequency control in radios, televisions, and other electronic communications equipment and for crystal-controlled clocks and watches.
Any one of the forms of silicon dioxide (SiO2), including quartz, tridymite, cristobalite, coesite, stishovite, melanophlogite, lechatelierite, and chalcedony. Various kinds of silica minerals have been produced synthetically, among which are keatite and silicalite.
Except for stishovite, all silica minerals are made up of tetrahedral groups comprised of four oxygen atoms surrounding a central silicon. Each tetrahedral group shares an oxygen atom with another tetrahedral group, forming a three-dimensional structure. The principal difference among the various silica minerals is the detailed geometry of the arrangement of tetrahedra, which gives rise to different crystal structures and thus physical properties. Quartz has a relatively dense packing of tetrahedra compared to tridymite and cristobalite, which exhibit relatively large open cavities.
This packing difference is reflected in their densities: 2.65, 2.32, 2.26 grams per cubic centimetre for quartz, cristobalite, and tridymite, respectively.
Each of these three polymorphs of silica has a field of stability under equilibrium conditions, but because transformation from one structure to another is sluggish, tridymite and cristobalite are found within the stability field of quartz. Each of the polymorphs also has high- and low-temperature modifications that are only slightly different structurally. Therefore, under low-pressure conditions, low-quartz is stable until 573° C (1,063° F), at which point high-quartz becomes stable. At 867° C (1,593° F), high-quartz transforms to tridymite. The high-low transformations require only slight displacements of the tetrahedral groups and occur rapidly. Compositionally, quartz is usually quite pure, with only traces of other elements. In contrast, tridymite and cristobalite may contain up to about one percent by weight of impurities because of the open nature of their framework which easily accommodates other atoms, especially those of aluminum, sodium, potassium, and lithium.
Tridymite and cristobalite occur in volcanic rocks such as rhyolite and slowly invert to quartz polymorphs.
Of the other silica phases, coesite and stishovite are high-pressure polymorphs found where quartz was shocked by meteorite impact. Coesite also occurs in some eclogite xenoliths from the Earth's upper mantle. Stishovite is unlike other silica phases in that silicon is in octahedral rather than tetrahedral coordination, resulting in a high density of 4.3 g/cc. Keatite is a high-pressure polymorph, but it has not been found in nature.
Chalcedony is cryptocrystalline silica consisting of minute quartz crystals and submicroscopic pores. Melanophlogite has an open structure large enough to occlude sulfur species. Lechatelierite is silica glass (amorphous) and is only rarely found in nature.
Silicon, Si, is a non-metallic main group element, found in Group IVb of the periodic table.
Atomic Number : 14
Atomic Mass : 28.086
Silicon in the amorphous form was prepared by Berzelius in 1823AD
Silicon in the crystalline form was prepared by H St Cdeville in 1854AD.
Silicon is the most abundant element on Earth after oxygen.
Silicon exists primarily as silica (in the free state as Quartz, Flint and Sand), and combined with other materials as
Felspar or Orthoclase, K2O.Al2O3.6SiO2,
Kaolinite, Al2O3.2SiO2.2H2O, and
Amorphous Silicon is prepared in the laboratory by heating potassium in an atmosphere of silicon tetrafluoride.
SiF4 + 4 K ==> Si + 4 HF
Crystalline Silicon is prepared in the laboratory by dissolving silicon in aluminium and then cooling the solution, when crystalline silicon separates out of the solution.
Silicon exists in different allotropic forms which differ in chemical and physical properties.
is a dark brown powder which on heating in air forms a protective coating of silica which prevents further oxidation,
is insoluble in water and most acids, and
dissolves in hydrofluoric Acid forming fluorosilicic acid.
Si + 3 HCl ==> 2 H2 + H2SiF6
dissolves in sodium hydroxide forming sodium silicate.
Si + 2 NaOH + H2O ==> 2 H2 + Na2SiO3
resembles amorphous silicon in many of its chemical reactions but it is less reactive,
consists of dark-gray needles or octahedral plates, which are hard enough to scratch glass.
Properties of Silicon Dioxide
Silica is a transparent solid with high melting point.
Silica is inert to most chemical reagents but reacts with hydrogen fluoride to form silicon tetrafluoride, which is a colourless gas at room temperature and water.
Silica is an acidic oxide, which reacts with alkalis to form salt and water.
SiO2 + 2NaOH ==> Na2SiO3 + H2O
Silicon dioxide is a crystalline compound that transmits visible and ultraviolet light. Many crystalline forms exist, the most common of which is Quartz.
Under exposure to oxygen, a silicon surface oxidizes to form silicon dioxide (SiO2). Native silicon dioxide is a high-quality electrical insulator and can be used as a barrier material during impurity implants or diffusion, for electrical isolation of semiconductor devices, as a component in MOS transistors, or as an interlayer dielectric in multilevel metallization structures such as multichip modules. The ability to form a native oxide was one of the primary processing considerations which led to silicon becoming the dominant semiconductor material used in integrated circuits today.
Thermal oxidation of silicon is easily achieved by heating the substrate to temperatures typically in the range of 900-1200 degrees C. The atmosphere in the furnace where oxidation takes place can either contain pure oxygen or water vapor. Both of these molecules diffuse easily through the growing SiO2 layer at these high temperatures. Oxygen arriving at the silicon surface can then combine with silicon to form silicon dioxide.
Additional variety specimens include:
Quartz is the most common mineral on the face of the Earth. It is found in nearly every geological environment and is at least a component of almost every rock type. It frequently is the primary mineral, >98%. It is also the most varied in terms of varieties, colors and forms. This variety comes about because of the abundance and widespread distribution of quartz. A collector could easily have hundreds of quartz specimens and not have two that are the same due to the many broad catagories. The specimens could be separated by answers to the following questions: color ?, shade?, pyramidal ?, prismatic ?, druzy ?, twinned ?, sceptered ?, phantomed ?, included ?, tapered?, coated?, microcrystalline?, stalactitic ?, concretionary ?, geoidal ?, banded?, etc. Multiple combinations of these could produce hundreds of unique possibilities.
Some macrocrystalline (large crystal) varieties are well known and popular as ornamental stone and as gemstones.
Amethyst is the purple gemstone variety.
Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst.
Milky Quartz is the cloudy white variety.
Rock crystal is the clear variety that is also used as a gemstone.
Rose quartz is a pink to reddish pink variety.
Smoky quartz is the brown to gray variety.
Cryptocrystalline (crystals too small to be seen even by a microscope) varieties are also used as semi-precious stones and for ornamental purposes. These varieties are divided more by character than by color. Chalcedony or agate is divided into innumeral types that have been named for locally common varieties. Some of the more beautiful types have retained their names on a world-wide basis while other names have faded into obscurity. Some of the more common of these types are chrysoprase (a pure green agate), sard (a yellow to brown agate), sardonyx (banded sard), onyx (black and white agate), carnelian (a yellow to orange agate), flint (a colorful and microscopically fibrous form), jasper (a colorful impure agate) and bloodstone (a green with red speckled agate).
Quartz is not the only mineral composed of SiO 2.There are no less than eight other known structures that are composed of SiO 2.These other substances and quartz are polymorphs of silicon dioxide and belong to an informal group called the Quartz Group or Silica Group. All members of this group, except quartz, are uncommon to extemely rare on the surface of the earth and are stable only under high temperatures and high pressures or both. These minerals have their own unique structures although they share the same chemistry, hence the term polymorph, which means many forms .
Quartz has a unique structure. Actually, there is another mineral that shares quartz's structure, and it is not even a silicate. It is a rare phosphate named berlinite ,AlPO 4,that is isostructural with quartz. The structure of quartz involves corkscrewing (helix) chains of silicon tetrahedrons. The corkscrew takes four tetrahedrons in order to repeat itself, or three turns. Each tetrahedron is essentially rotated 120 degrees. The chains are aligned along the Caxis of the crystal and interconnected to two other chains at each tetrahedron making quartz a true tectosilicate . This structure is not like the structure of the chain silicates or inosilicates whose silicate tetrahedronal chains are not directly connected to each other. The structure of quartz helps explain many of its physical attributes.
For one, the helix makes three turns and this helps produce the trigonal symmetry of quartz. Likewise a helix or corkscrew lacks mirror planes of symmetry as does quartz. The corkscrew structure would also disrupt any cleavage which requires a plane of weakness not found in quartz and breakage would result in the curved fracture, conchoidal , that is found in quartz. Quartz can also have left and right handed crystals just as a corkscrew can screw in a left handed way or in a right handed way. There are even some very difficult to identify crystals of quartz that are twinned with alternating one sixths of the crystal being right handed and then left handed.
Quartz is a fun mineral to collect. Its abundance on the Earth's surface is incredible and produces some wonderful varieties that don't even look like the same mineral. A collector must always be up on the many varieties of quartz and it sometimes embarrasses a collector to have collected too many specimens of such a common mineral. But nearly all collectors concede that you can never really have enough quartz specimens.
Color is as variable as the spectrum, but clear quartz is by far the most common color followed by white or cloudy (milky quartz). Purple (Amethyst), pink (Rose Quartz), gray or brown to black (Smoky Quartz) are also common. Cryptocrystalline varieties can be multicolored.
Luster is glassy to vitreous as crystals, while cryptocrystalline forms are usually waxy to dull but can be vitreous.
Transparency: Crystals are transparent to translucent, cryptocrystalline forms can be translucent or opaque.
Crystal System is trigonal; 3 2 .
Crystal Habits are again widely variable but the most common habit is hexagonal prisms terminated with a six sided pyramid (actually two rhombohedrons ). Three of the six sides of the pyramid may dominate causing the pyramid to be or look three sided. Left and right handed crystals are possible and identifiable only if minor trigonal pyramidal faces are present. Druse forms (crystal lined rock with just the pyramids showing) are also common. Massive forms can be just about any type but common forms include botryoidal, globular, stalactitic, crusts of agate such as lining the interior of a geode and many many more.
Cleavage is very weak in three directions (rhombohedral).
Fracture is conchoidal.
Hardness is 7,less in cryptocrystalline forms.
Specific Gravity is 2.65 or less if cryptocrystalline. (average)
Streak is white.
Other Characteristics: Striations on prism faces run perpendicular to C axis, piezoelectric (see tourmaline ) and index of refraction is 1.55 .
Associated Minerals are numerous and varied but here are some of the more classic associations of quartz (although any list of associated minerals of quartz is only a partial list): amazonite a variety of microcline ,tourmalines especially elbaite ,wolframite ,pyrite ,rutile ,zeolites ,fluorite ,calcite ,gold ,muscovite ,topaz ,beryl ,hematite and spodumene .
Notable Occurrences of amethyst are Brazil, Uraguay, Mexico, Russia, Thunder Bay area of Canada, and some locallities in the USA. For Smoky Quartz; Brazil, Colorado, Scotland, Swiss Alps among many others. Rose Quartz is also wide spread but large quantities come from brazil as do the only large find of Rose Quartz prisms. Natural citrine is found with many amethyst deposits but in very rare quantities. Fine examples of Rock crystal come from Brazil (again), Arkansas, many locallities in Africa, etc. Fine Agates are found in, of course, Brazil, Lake Superior region, Montana, Mexico and Germany.
Best Field Indicators are first the fact that it is very common (always assume transparent clear crystals may be quartz), crystal habit, hardness, striations, good conchoidal fracture and lack of good cleavage.