Everything about Quartz totally explained
Quartz (from
German ) is the most abundant
mineral in the
Earth's
continental crust (although
feldspar is more common in the world as a whole). It is made up of a
lattice of
silica tetrahedra. Quartz has a hardness of 7 on the
Mohs scale and a
density of 2.65 g/cm³.
Crystal habit
Quartz belongs to the
rhombohedral crystal system. The
ideal crystal shape is a six-sided
prism terminating with six-sided
pyramids at each end. In nature quartz crystals are often
twinned, distorted, or so intergrown with adjacent crystals of quartz or other minerals as to only show part of this shape, or to lack obvious crystal faces altogether and appear massive. Well-formed crystals typically form in a 'bed' that has unconstrained growth into a void, but because the crystals must be attached at the other end to a matrix, only one termination pyramid is present. A quartz
geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward.
Varieties
Pure quartz is colorless or white, colored varieties include rose quartz,
amethyst, smoky quartz, milky quartz, and others. Quartz goes by an array of different names. The most important distinction between types of quartz is that of
macrocrystalline (individual crystals visible to the unaided eye) and the
microcrystalline or
cryptocrystalline varieties (aggregates of crystals visible only under high magnification).
Chalcedony is a generic term for cryptocrystalline quartz. The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline.
Although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is a secondary identifier for the cryptocrystalline minerals, although it's a primary identifier for the macrocrystalline varieties. This doesn't always hold true.
| Chalcedony |
Any cryptocrystalline quartz, although generally only used for white or lightly colored material. Otherwise more specific names are used. |
| Agate |
Multi-colored, banded chalcedony, semi-translucent to translucent |
| Onyx |
Agate where the bands are straight, parallel and consistent in size. |
| Jasper |
Opaque chalcedony, typically red to brown |
| Aventurine |
Translucent chalcedony with small inclusions (usually mica) that shimmer. |
| Tiger's eye |
Fibrous gold to red-brown coloured quartz, exhibiting chatoyancy. |
| Rock crystal |
Clear, colorless |
| Amethyst |
Purple, transparent |
| Citrine |
Yellow to reddish orange to brown, greenish yellow |
| Prasiolite |
Mint green, transparent |
| Rose quartz |
Pink, translucent, may display diasterism |
| Rutilated quartz |
Contains acicular (needles) inclusions of rutile |
| Milk quartz |
White, translucent to opaque, may display diasterism |
| Smoky quartz |
Brown to grey, opaque |
| Morion |
Dark-brown, opaque |
| Carnelian |
Reddish orange chalcedony, translucent |
Image:IMG 5779.jpg|Rose quartz
Image:QuartzUSGOV.jpg|Milk quartz
Image:Kwarc z rutylem.JPG|Rutilated quartz crystal
Synthetic and artificial treatments
Not all varieties of quartz are naturally occurring.
Prasiolite, an olive colored material, is produced by heat treatment; natural prasiolite has also been observed in Lower Silesia in Poland. Although
citrine occurs naturally, the majority is the result of heat-treated amethyst.
Carnelian is widely heat-treated to deepen its color.
Due to natural quartz being so often
twinned, much of the quartz used in industry is synthesized. Large, flawless and untwinned crystals are produced in an
autoclave via the
hydrothermal process;
emeralds are also synthesized in this fashion. While these are still commonly referred to as quartz, the correct term for this material is
silicon dioxide.
Occurrence
Quartz occurs in
hydrothermal veins and
pegmatites. Well-formed crystals may reach several meters in length and
weigh hundreds of kilograms. These veins may bear
precious metals such as
gold or
silver, and form the quartz ores sought in
mining. Erosion of pegmatites may reveal expansive pockets of crystals, known as "cathedrals."
Quartz is a common constituent of
granite,
sandstone,
limestone, and many other
igneous,
sedimentary, and
metamorphic rocks.
Related silica minerals
Tridymite and
cristobalite are high-temperature
polymorphs of SiO
2 that occur in high-silica
volcanic rocks.
Coesite is a denser polymorph of quartz found in some meteorite impact sites and in metamorphic rocks formed at pressures greater than those typical of the Earth's crust.
Stishovite is a yet denser and higher-pressure polymorph of quartz found in some meteorite impact sites.
Lechatelierite is an
amorphous silica
glass SiO
2 which is formed by
lightning strikes in quartz
sand.
History
The name "quartz" comes from the German "Quarz", which is of Slavic origin (Czech miners called it
křemen). Other sources insist the name is from the
Saxon word "Querkluftertz", meaning
cross-vein ore.
Quartz is the most common material identified as the mystical substance
maban in
Australian Aboriginal mythology. It is found regularly in passage tomb cemeteries in Europe in a burial context, eg.
Newgrange or
Carrowmore in the
Republic of Ireland. The
Irish word for quartz is
grian cloch, which means 'stone of the sun'.
Roman naturalist
Pliny the Elder believed quartz to be water
ice, permanently frozen after great lengths of time. (The word "crystal" comes from the Greek word for ice.) He supported this idea by saying that quartz is found near glaciers in the Alps, but not on volcanic mountains, and that large quartz crystals were fashioned into spheres to cool the hands. He also knew of the ability of quartz to split light into a
spectrum. This idea persisted until at least the 1600s.
Nicolas Steno's study of quartz paved the way for modern
crystallography. He discovered that no matter how distorted a quartz crystal, the long prism faces always made a perfect 60 degree angle.
Charles Sawyer invented the commercial quartz crystal manufacturing process in
Cleveland,
Ohio,
United States. This initiated the transition from mined and cut quartz for electrical appliances to manufactured quartz.
Quartz's
piezoelectric properties were discovered by
Jacques and
Pierre Curie in 1880. The
quartz oscillator or resonator was first developed by
Walter Guyton Cady in 1921
(External Link
). George Washington Pierce designed and patented quartz crystal oscillators in 1923
(External Link). Warren Marrison created the first quartz oscillator clock based on the work of Cady and Pierce in 1927
(External Link).
Quartz crystals are rotary polar (see
rotary polarization) and have the ability to rotate the plane of polarization of light passing through them. They are also highly piezoelectric, becoming polarized with a negative charge on one end and a positive charge on the other when subjected to pressure. They will vibrate if an alternating electric current is applied to them. This proves them to be highly important in commerce for making pressure gauges, oscillators, resonators and watches.
Piezoelectricity
Quartz crystals have
piezoelectric properties, that's they develop an electric potential upon the application of mechanical stress. An early use of this property of quartz crystals was in
phonograph pickups. One of the most common piezoelectric uses of quartz today is as a
crystal oscillator. The
quartz clock is a familiar device using the mineral. The resonant frequency of a quartz crystal oscillator is changed by mechanically loading it, and this principle is used for very accurate measurements of very small mass changes in the
quartz crystal microbalance and in
thin-film thickness monitors.
Further Information
Get more info on 'Quartz'.
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