Quartz
Quartz is the most abundant mineral on earth (about 12% vol.), made of trigonal-crystallized silica (silicon dioxide, SiO2), with a hardness of 7 on the Mohs scale. The typical shape is a six-sided prisms that end in six-sided pyramids, although these are often distorted, or so massive that only part of the shape is apparant from a mined specimin. Additionally a bed is a common form, particulaly for varieties such as amethyst, where the crystals grow up from a matrix and thus only one termination pyramid is present. A quartz geode consists of a hollow pebble (usually an approximatly spherical shape), its core lined with a bed of crystals.
Being one of the most common minerals, quartz goes by a bewildering 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, whilst the transparent varieties tend to be macrocrystalline.
Although many of the varietal names historically arose from the colour of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Colour is a secondary identifier for the cryptocrystalline minerals, whilst colour is a primary identifier for the macrocrystalline varieties. This does not always hold true, however.
Major varieties of quartz
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Chalcedony
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Any cryptocrystalline quartz, although generally only used for white or lightly coloured material. Otherwise more specific names are used.
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Agate
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Banded Chalcedony, translucent
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Onyx
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Agate where the bands are staight, parallel and consistent in size.
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Jasper
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Opaque chalcedony, impure
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Aventurine
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Translucent chalcedony with small inclusions (usually mica) that shimmer.
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Tiger's eye
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Fibrous quartz, exhibiting chatoyancy.
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Rock Crystal
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Clear, colourless
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Amethyst
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Purple, transparent
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Citrine
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Yellow to reddish orange, greenish yellow
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Rose quartz
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Pink, translucent, may display diasterism
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Milk quartz, or snow quartz
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White, translucent to opaque, may display diasterism
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Carnelian
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Reddish orange chalcedony, translucent
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Not all varieties of quartz are naturally occurring. Prasiolite, an olive coloured material is produced by heat treatment. Although most citrine occurs naturally, most is the result of heat-treated amethyst. Carnelian is widely heat-treated to deepen its colour.
Because natural quartz is so often twinned, much 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.
Quartz occurs in hydrothermal veins and pegmatites. Well-formed crystals may reach several metres in length and weigh hundreds of kilograms. Erosion of pegmatites may reveal expansive pockets of crystals, known as "cathedrals."
Quartz is a common constituent of granite, sandstone and limestone.
Some quartz crystal structures are piezoelectric and are used as oscillators in electronic devices such as quartz clocks and radios.
A non-crystalline (glass) form of quartz, called fused quartz, can also be produced, distinct from typical window glass.
See also: list of minerals
Quartz is also the name for a display technology.
External links
Referenced By
Basanite | Carbon (Mac OS X) | Carbon (computing) | Electrical resistivity | Fused silica | Gabbro | Gemstone | Jaguar (macos) | Jewel | Latite | List of chemistry topics | List of minerals | MAC OS X | MacOS X | Mac OS/OS X | Mac OS 10 | Mac OS X/Carbon | Mac OS X 10 | Mohs Scale | Mohs hardness scale | Mohs scale of mineral hardness | OS X | Panther (macos) | Phonolite | Resistivity | Schist | Silica | Silicate | Silicon dioxide | Tephrite | Thermal conductance | Thermal conductivity | Trachyte | Watt per meter-kelvin | Watt per metre-kelvin
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