Pegmatite

Pegmatite with blue corundum crystals

Pegmatite containing lepidolite, tourmaline, and quartz from the White Elephant Mine in the Black Hills, South Dakota

A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size;^[1] such rocks are referred to as pegmatitic.
Most pegmatites are composed of quartz, feldspar and mica; in essence a granite. Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene and other minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions.
Crystal size is the most striking feature of pegmatites, with crystals usually over 5 cm in size. Individual crystals over 10 metres across have been found, and the world's largest crystal was found within a pegmatite.^{[citation needed]}
Similarly, crystal texture and form within pegmatitic rock may be taken to extreme size and perfection. Feldspar within a pegmatite may display exaggerated and perfect twinning, exsolution lamellae, and when affected by hydrous crystallization, macroscale graphic texture is known, with feldspar and quartz intergrown. Perthite feldspar within a pegmatite often shows gigantic perthitic texture visible to the naked eye.

Contents 1 General description 2 Petrology 3 Mineralogy 4 Geochemistry 5 Economic importance 6 Nomenclature 7 Occurrence 8 References 9 Further reading

General description

There is no single feature that is diagnostic to all pegmatites. Therefore, a list of criteria is used to distinguish them from other rocks. A very diagnostic feature are crystals that are larger than in normal igneous rocks. Pegmatites are usually small compared to typical intrusions. Their size is in the order of magnitude of 1 m to a few 100 m. Compared to typical igneous rocks they are rather inhomogeneous and usually show zones with different mineral assemblages. Crystal size and mineral assemblages are usually oriented parallel to the wall rock or even concentric for pegmatite lenses.^[2]

Petrology

Crystal growth rates in pegmatite must be incredibly fast to allow gigantic crystals to grow within the confines and pressures of the Earth's crust. For this reason, the consensus on pegmatitic growth mechanisms involves a combination of the following processes;

• Low rates of nucleation of crystals coupled with high diffusivity to force growth of a few large crystals instead of many smaller crystals
• High vapor and water pressure, to assist in the enhancement of conditions of diffusivity
• High concentrations of fluxing elements such as boron and lithium which lower the temperature of solidification within the magma or vapor
• Low thermal gradients coupled with a high wall rock temperature, explaining the preponderance for pegmatite to occur only within greenschist metamorphic terranes

Despite this consensus on likely chemical, thermal and compositional conditions required to promote pegmatite growth there are three main theories behind pegmatite formation;

Theory name	Theory
Metamorphic	pegmatite fluids are created by devolatilisation (dewatering) of metamorphic rocks, particularly felsic gneiss, to liberate the right constituents and water, at the right temperature
Magmatic	pegmatites tend to occur in the aureoles of granites in most cases, and are usually granitic in character, often closely matching the compositions of nearby granites. Pegmatites thus represent exsolved granitic material which crystallises in the country rocks
Metasomatic	pegmatite, in a few cases, could be explained by the action of hot alteration fluids upon a rock mass, with bulk chemical and textural change.

Metasomatism is currently not well favored as a mechanism for pegmatite formation and it is likely that metamorphism and magmatism are both contributors toward the conditions necessary for pegmatite genesis.

Mineralogy

Pegmatitic granite, Rock Creek Canyon, eastern Sierra Nevada, California. Note pink potassium feldspars and cumulate-filled chamber.

The mineralogy of a pegmatite is in all cases dominated by some form of feldspar, often with mica and usually with quartz, being altogether "granitic" in character. Beyond that, pegmatite may include most minerals associated with granite and granite-associated hydrothermal systems, granite-associated mineralisation styles, for example greisens, and somewhat with skarn associated mineralisation.
It is however impossible to quantify the mineralogy of pegmatite in simple terms because of their varied mineralogy and difficulty in estimating the modal abundance of mineral species which are of only a trace amount. This is because of the difficulty in counting and sampling mineral grains in a rock which may have crystals from centimeters to meters across.
Garnet, commonly almandine or spessartine, is a common mineral within pegmatites intruding mafic and carbonate-bearing sequences. Pegmatites associated with granitic domes within the Archaean Yilgarn Craton intruding ultramafic and mafic rocks contain red, orange and brown almandine garnet.
Tantalum and niobium minerals (columbite, tantalite, niobite) are found in association with spodumene, lepidolite, tourmaline, cassiterite in the massive Greenbushes Pegmatite in the Yilgarn Craton of Western Australia, considered a typical metamorphic pegmatite unassociated with granite.

Geochemistry

Pegmatite is difficult to sample representatively due to the large size of the constituent mineral crystals. Often, bulk samples of some 50–60 kg of rock must be crushed to obtain a meaningful and repeatable result. Hence, pegmatite is often characterised by sampling the individual minerals which comprise the pegmatite, and comparisons are made according to mineral chemistry.
Geochemically, pegmatites typically have major element compositions approximating "granite", however, when found in association with granitic plutons it is likely that a pegmatite dike will have a different trace element composition with greater enrichment in large-ion lithophile (incompatible) elements, boron, beryllium, aluminium, potassium and lithium, uranium, thorium, cesium, et cetera.
Occasionally, enrichment in the unusual trace elements will result in crystallisation of equally unusual and rare minerals such as beryl, tourmaline, columbite, tantalite, zinnwaldite and so forth. In most cases, there is no particular genetic significance to the presence of rare mineralogy within a pegmatite, however it is possible to see some causative and genetic links between, say, tourmaline-bearing granite dikes and tourmaline-bearing pegmatites within the area of influence of a composite granite intrusion (Mount Isa Inlier, Queensland, Australia).

Economic importance

Pegmatites are important because they often contain rare earth minerals and gemstones, such as aquamarine, tourmaline, topaz, fluorite, apatite and corundum, often along with tin and tungsten minerals, among others.
Pegmatites are the primary source of lithium either as spodumene, lithiophyllite or usually from lepidolite. The primary source for caesium is pollucite, a mineral from a zoned pegmatite. The majority of the world's beryllium is sourced from non-gem quality beryl within pegmatite. Tantalum, niobium, rare-earth elements are sourced from a few pegmatites worldwide, notably the Greenbushes Pegmatite. Bismuth, molybdenum and tin have been won from pegmatite, but this is not yet an important source of these metals.

Nomenclature

Pegmatites can be classified according to the elements or mineral of interest, for instance "lithian pegmatite" to describe a Li-bearing or Li-mineral bearing pegmatite, or "boron pegmatite" for those containing tourmaline.
There is often no meaningful way to distinguish pegmatites according to chemistry due to the difficulty of obtaining a representative sample, but often groups of pegmatites can be distinguished on contact textures, orientation, accessory minerals and timing. These may be named formally or informally as a class of intrusive rock or within a larger igneous association.
While difficult to be certain of derivation of pegmatite in the strictest sense, often pegmatites are referred to as "metamorphic", "granitic" or "metasomatic", based on the interpretations of the investigating geologist.

Occurrence

Worldwide, notable pegmatite occurrences are within the major cratons, and within greenschist-facies metamorphic belts. However, pegmatite localities are only well recorded when economic mineralisation is found.
Within the metamorphic belts, pegmatite tends to concentrate around granitic bodies within zones of low mean strain and within zones of extension, for example within the strain shadow of a large rigid granite body. Similarly, pegmatite is often found within the contact zone of granite, transitional with some greisens, as a late-stage magmatic-hydrothermal effect of syn-metamorphic granitic magmatism. Some skarns associated with granites also tend to host pegmatites.
Aplite and porphyry dikes and veins may intrude pegmatites and wall rocks adjacent to intrusions, creating a confused sequence of felsic intrusive apophyses (thin branches or offshoots of igneous bodies) within the aureole of some granites.

References

Wikimedia Commons has media related to: Pegmatite

1. ^ USGS pegmatite definition, retrieved 2009-08-28
2. ^ London, D.; Kontak, D. J. (3 September 2012). "Granitic Pegmatites: Scientific Wonders and Economic Bonanzas". Elements 8 (4): 257–261. doi:10.2113/gselements.8.4.257.

Further reading

• London, D. (2008): Pegmatites. Canadian Mineralogist Special Publication 10, 347 pp.
• Tan, Li-ping, 1966, Major Pegmatite Deposits of New York State, New York State Museum Bulletin No. 408
• Pegmatopia: David London, School of Geology & Geophysics, University of Oklahoma

[hide] v t e Igneous rocks by composition Type Ultramafic <45% SiO2 Mafic 45–52% SiO2 Intermediate 52–63% SiO2 Intermediate-Felsic 63–69% SiO2 Felsic >69% SiO2 Volcanic rocks: Subvolcanic rocks: Plutonic rocks: Komatiite, Picrite basalt Kimberlite, Lamproite Peridotite Basalt Diabase (Dolerite) Gabbro Andesite Diorite Dacite Granodiorite Rhyolite Aplite—Pegmatite Granite

Categories:

• Igneous rocks
• Economic geology
• Phaneritic rocks

Pegmatito

Pegmatito composto de feldspato alterado e cristais azuis de corindo (maciço alcalino de Canaã, Rio de Janeiro, Brasil)

Pegmatito, pegmatite ou pegmatita, é a designação dada a uma rocha ígnea de grão grosseiro em o que o tamanho dos grãos (minerais) é igual ou maior que 20 mm. Diz-se que estas rochas apresentam textura pegmatítica.
A maioria dos pegmatitos apresentam mineralogia semelhante ao granito e mais raramente a outras rochas ígneas intrusivas de que sejam derivados. Apresentam com frequência quartzo, feldspatos e micas, mas paragéneses exóticas podem ocorrer também. Os pegmatitos são importantes porque frequentemente contêm outros minerais de terras raras e gemas como água-marinha, turmalina, topázio, fluorite e apatite, muitas vezes acompanhados por minerais de estanho e tungsténio, entre outros. É possível encontrar cristais com mais de 10 metros de dimensão máxima.
Existem pegmatitos graníticos, pegmatitos boro-graníticos, pegmatitos litíferos e pegmatitos boro-litíferos.
Nas primeiras aulas de geologia, os estudantes aprendem que cristais de grandes dimensões resultam do arrefecimento lento dos magmas, e que cristais mais pequenos são resultado de arrefecimentos mais rápidos. Os pegmatitos são uma excepção a esta regra.
Os pegmatitos são formados a partir de magma que arrefeceu muito rapidamente, às vezes em poucos dias. Frequentemente, acontece que um dique ou uma soleira de magma intrui rochas muito mais frias sem atingir a superfície. Por razões ainda não bem compreendidas, esta rocha consegue desenvolver grandes cristais apesar do seu rápido arrefecimento. Isto parece dever-se à acção da água, que é muito importante em todas as reacções cristalinas.
Apesar do seu rápido arrefecimento, os pegmatitos podem ter grandes cristais, às vezes atingindo vários metros de extensão. Por accção da água podem também ser concentrados elementos mais raros nos pegmatitos. Consequentemente, não é raro encontrar minerais raros ou até gemas em pegmatitos. Os pegmatitos são também uma fonte de minerais de terras raras como a columbite e a tantalite.
Os pegmatitos tendem a formar veios ou bandas espessas em granitos. De facto, a sua ocorrência é mais frequente em intrusões graníticas em granitos pré-existentes, conhecidas por diques pegmatíticos. Podem também formar-se bolsadas contendo cristais perfeitamente formados. Isto ocorre porque os cristais são livres de desenvolver-se no espaço vazio da bolsada sem amontoamento ou distorção.
As maiores províncias pegmatíticas do mundo situam-se no Brasil (Minas Gerais e Borborema) e Afeganistão. A maioria das gemas associadas a pegmatitos são provenientes do Brasil.

[Esconder] v • e Rochas ígneas por composição
Tipo Ultramáfica < 45% SiO2 Máfica 45-52% SiO2 Intermédia 52–63% SiO2 Intermédia-Félsica 63–69% SiO2 Félsica >69 % SiO2 Rochas vulcânicas: Rochas subvulcânicas: Rochas plutônicas: Komatiito, Basalto picrítico Kimberlito, Lamproíto Peridotito Basalto Diábase Gabro Andesito Diorito—Sienito Dacito Granodiorito Riólito—Obsidiana Aplito—Pegmatito Granito

Categorias:

• Rochas ígneas
• Geologia económica

Rutile

Rutile
Wine-red rutile crystals from Binn Valley in Switzerland (Size: 2.0 x 1.6 x 0.8 cm)
General
Category	Oxide minerals
Formula (repeating unit)	TiO2
Strunz classification	04.DB.05
Crystal symmetry	Tetragonal 4/m 2/m 2/m; space group 136
Unit cell	a = 4.5937 Å, c = 2.9587 Å; Z = 2
Identification
Color	Reddish brown, red, pale yellow, pale blue, violet, rarely grass-green; black if high in Nb–Ta
Crystal habit	Acicular to Prismatic crystals, elongated and striated parallel to [001]
Crystal system	Tetragonal ditetragonal dipyramidal
Twinning	Comon on {011}, or {031}; as contact twins with two, six, or eight individuals, cyclic, polysynthetic
Cleavage	{110} good, 100 moderate, parting on {092} and {011}
Fracture	Uneven to sub-conchoidal
Mohs scale hardness	6.0 - 6.5
Luster	Adamantine to submetallic
Streak	Bright red to dark red
Diaphaneity	Opaque, transparent in thin fragments
Specific gravity	4.23 increasing with Nb–Ta content
Optical properties	Uniaxial (+)
Refractive index	nω = 2.605–2.613 nε = 2.899–2.901
Birefringence	0.2870-0.2940
Pleochroism	Weak to distinct brownish red-green-yellow
Dispersion	strong
Fusibility	Fusible in alkali carbonates
Solubility	Insoluble in acids
Common impurities	Fe, Nb, Ta
References	[1][2][3][4]

Rutile is a mineral composed primarily of titanium dioxide, TiO₂.
Rutile is the most common natural form of TiO₂. Two rarer polymorphs of TiO₂ are known:

• Anatase (sometimes known by the obsolete name "octahedrite"), a tetragonal mineral of pseudo-octahedral habit
• Brookite, an orthorhombic mineral

Rutile has among the highest refractive indices of any known mineral and also exhibits high dispersion. Natural rutile may contain up to 10% iron and significant amounts of niobium and tantalum.
Rutile derives its name from the Latin rutilus, red, in reference to the deep red color observed in some specimens when viewed by transmitted light.

Contents 1 Occurrence 2 Crystal structure 3 Uses and economic importance 4 Synthetic rutile 5 See also 6 References 7 External links

Occurrence

Rutile output in 2005

Rutile is a common accessory mineral in high-temperature and high-pressure metamorphic rocks and in igneous rocks.
Thermodynamically, rutile is the most stable polymorph of TiO₂ at all temperatures, exhibiting lower total free energy than metastable phases of anatase or brookite.^[5] Consequently, the transformation of the metastable TiO₂ polymorphs to rutile is irreversible. As it has the lowest molecular volume of the three main polymorphs; it is generally the primary titanium bearing phase in most high-pressure metamorphic rocks, chiefly eclogites.

Rutile in quartz

Within the igneous environment, rutile is a common accessory mineral in plutonic igneous rocks, though it is also found occasionally in extrusive igneous rocks, particularly those that have deep mantle sources such as kimberlites and lamproites. Anatase and brookite are found in the igneous environment particularly as products of autogenic alteration during the cooling of plutonic rocks; anatase is also found in placer deposits sourced from primary rutile.
The occurrence of large specimen crystals is most common in pegmatites, skarns, and granite greisens. Rutile is found as an accessory mineral in some altered igneous rocks, and in certain gneisses and schists. In groups of acicular crystals it is frequently seen penetrating quartz as in the fléches d'amour from Graubünden, Switzerland. In 2005 the Republic of Sierra Leone in West Africa had a production capacity of 23% of the world's annual rutile supply, which rose to approximately 30% in 2008. The reserves, lasting for about 19 years, are estimated at 259,000,000 metric tons (285,000,000 short tons).^[6]

Crystal structure

The unit cell of rutile. Ti atoms are gray; O atoms are red.

Rutile has a primitive tetragonal unit cell, with unit cell parameters a=b=4.584Å, and c=2.953Å.^[7] The titanium cations have a coordination number of 6 meaning they are surrounded by an octahedron of 6 oxygen atoms. The oxygen anions have a co-ordination number of 3 resulting in a trigonal planar co-ordination. Rutile also shows a screw axis when its octahedron are viewed sequentially.^[8]

Uses and economic importance

Acicular crystals of rutile protruding from a quartz crystal

In large enough quantities in beach sands, rutile forms an important constituent of heavy minerals and ore deposits. Miners extract and separate the valuable minerals—e.g., rutile, zircon, and ilmenite. The main uses for rutile are the manufacture of refractory ceramic, as a pigment, and for the production of titanium metal.
Finely powdered rutile is a brilliant white pigment and is used in paints, plastics, paper, foods, and other applications that call for a bright white color. Titanium dioxide pigment is the single greatest use of titanium worldwide. Nanoscale particles of rutile are transparent to visible light but are highly effective in the absorption of ultraviolet radiation. The UV absorption of nano-sized rutile particles is blue-shifted compared to bulk rutile, so that higher-energy UV light is absorbed by the nanoparticles. Hence, they are used in sunscreens to protect against UV-induced skin damage.
Small rutile needles present in gems are responsible for an optical phenomenon known as asterism. Asteriated gems are known as "star" gems. Star sapphires, star rubies, and other "star" gems are highly sought after and are generally more valuable than their normal counterparts.
Rutile is widely used as a welding electrode covering. It is also used as a part of the ZTR index, which classifies highly weathered sediments.

Synthetic rutile

Synthetic rutile was first produced in 1948 and is sold under a variety of names. Very pure synthetic rutile is transparent and almost colorless (slightly yellow) in large pieces. Synthetic rutile can be made in a variety of colors by doping, although the purest material is almost colorless. The high refractive index gives an adamantine luster and strong refraction that leads to a diamond-like appearance. The near-colorless diamond substitute is sold as "Titania", which is the old-fashioned chemical name for this oxide. However, rutile is seldom used in jewellery because it is not very hard (scratch-resistant), measuring only about 6 on the Mohs hardness scale.

See also

• List of minerals

References

1. ^ Handbook of Mineralogy
2. ^ Webmineral data
3. ^ Mindat.org
4. ^ Klein, Cornelis and Cornelius S. Hurlbut, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York, p. 304-305, ISBN 0-471-80580-7
5. ^ Hanaor, D. A. H.; Assadi, M. H. N.; Li, S.; Yu, A.; Sorrell, C. C. (2012). "Ab initio study of phase stability in doped TiO₂". Computational Mechanics 50 (2): 185–194. doi:10.1007/s00466-012-0728-4.
6. ^ "Sierra Rutile Mine". Titanium Resources Group. Retrieved 2009-05-06.^{[dead link]}
7. ^ Diebold, Ulrike (2003). "The surface science of titanium dioxide". Surface Science Reports 48 (5-8): 53–229. Bibcode:2003SurSR..48...53D. doi:10.1016/S0167-5729(02)00100-0.

Rutilo

Rutilo
Classificação Strunz	IV/D.02-10
Cor	rosso brunastro, nero
Fórmula química	TiO2
Propriedades cristalográficas
Sistema cristalino	tetragonale
Parâmetros da célula	a = 4,49, c = 2,96
Grupo espacial	P 4/mnm
Propriedades físicas
Densidade	4,18 - 4,25
Dureza	6 - 6,5
Clivagem	distinta secondo {110}
Fratura	Concoide
Brilho	adamantina o submetallica
Opacidade	traslucido o trasparente

Pendente de quartzo sagenítico, podendo observar-se os cristais aciculares de rutilo dispersos no interior do quartzo.

O rutilo ou rútilo é um mineral composto de dióxido de titânio , TiO₂, sendo um dos três polimorfos de TiO₂:

• Rutilo, um mineral usualmente tetragonal de hábito prismático, geralmente com cristais maclados;
• Anatase ou octaedrita , um mineral tetragonal de hábito octaédrico, e
• Brookita, um mineral ortorrômbico. A anatase e a brookita são minerais relativamente raros.

Índice 1 Propriedades físicas 2 Tipos de ocorrência 3 Rutilo sintético 4 Usos e aplicações 5 Etimologia

Propriedades físicas

O rutilo tem uma fratura subconcoidal, é fragil , com dureza 6 a 6,5 , densidade relativa 4,1 a 4,2 , brilho metálico a adamantino, geralmente de cor marrom ou vermelho, algumas vezes, amarelo, azul ou violeta. É transparente a opaco. O rutilo natural é geralmente opaco ou vermelho muito escuro. O rutilo pode pode conter até 10% de ferro. O rutilo é a forma mais estável de dióxido de titânio e é produzido em temperaturas mais altas, com a brookita formando-se em temparaturas mais baixas e, a octaedrita, em temperaturas ainda mais baixas.

Tipos de ocorrência

Tufo de rutilo acicular encravado em quartzo (originário do Brasil, actualmente no Museu de História Natural de Londres)

O rutilo é encontrado como mineral acessório em algumas rochas igneas alteradas, e em certos gnaisses e xistos cristalinos. Nos grupos de cristais aciculares é frequentemente encontrado incrustrado no quartzo como no "fléches d'amour" de Grisons, Suíça. Pequenas agulhas de rutilo encontrado em algumas gemas são responsáveis pelo fenômeno ópticos denominado asterismo, que aparece em safiras, rubis e outras pedras preciosas.

Rutilo sintético

O rutilo sintético foi produzido pela primeira vez em 1948 sendo comercializado sob vários nomes. Tem uma elevada dispersão óptica e um elevado índice de refração a luz, tão forte que demonstra ser falso, porém muito colorido. O rutilo sintético pode ser produzido em várias cores, porém nunca como branco transparente puro, sendo sempre levemente amarelo.

Usos e aplicações

Quando finamente moído o rutilo é usado como um brilhante pigmento branco , utilizado em tintas, plásticos, papel, alimentos e outras aplicações que requerem uma cor branca brilhante. Os pigmentos de dióxido de titânio são a principal aplicação do titânio a nível mundial, pois não é, para já, economicamente viável a produção de titânio metal a partir do rutilo. Nanopartículas de rutilo são transparentes para a luz visível mas altamente reflectoras de luz ultravioleta sendo por isso usadas no fabrico de protectores solares. Uma variedade sintética praticamente incolor, designada por titania, é comercializada como substituto de diamante.

Etimologia

O nome rutilo é derivado do latim rutilus, vermelho, em referência a cor vermelha profunda encontrada em alguns espécimes quando vistos sob a luz.

Jade

"Nephrite jade" redirects here. For nephrite itself, see Nephrite.

This article is about the gemstone. For other uses, see Jade (disambiguation).

A selection of antique, hand-crafted Chinese jade buttons

Unworked jade

Jade on display in Jade City, British Columbia, Canada

Jade is an ornamental stone. The term jade is applied to two different metamorphic rocks that are made up of different silicate minerals:

• Nephrite consists of a microcrystalline interlocking fibrous matrix of the calcium, magnesium-iron rich amphibole mineral series tremolite (calcium-magnesium)-ferroactinolite (calcium-magnesium-iron). The middle member of this series with an intermediate composition is called actinolite (the silky fibrous mineral form is one form of asbestos). The higher the iron content the greener the colour.
• Jadeite is a sodium- and aluminium-rich pyroxene. The gem form of the mineral is a microcrystalline interlocking crystal matrix.

Contents 1 Etymology 2 Overview 2.1 Nephrite and jadeite 2.2 Unusual varieties 3 History 3.1 Prehistoric and historic China 3.2 Prehistoric and historic India 3.3 Prehistoric and early historic Korea 3.4 Māori 3.5 Canada 3.6 Mesoamerica 4 Enhancement 5 See also 6 References 7 Further reading 8 External links

Etymology

The English word jade (alternative spelling "jaid") is derived (via French l'ejade and Latin ilia)^[1] from the Spanish term piedra de ijada (first recorded in 1565) or "loin stone", from its reputed efficacy in curing ailments of the loins and kidneys. Nephrite is derived from lapis nephriticus, the Latin version of the Spanish piedra de ijada.^[2]

Overview

Nephrite and jadeite

Nephrite and jadeite were used from prehistoric periods for hardstone carving. Jadeite has about the same hardness as quartz, while nephrite is somewhat softer. It was not until the 19th century that a French mineralogist determined that "jade" was in fact two different minerals.^{[citation needed]}
Among the earliest known jade artifacts excavated from prehistoric sites are simple ornaments with bead, button, and tubular shapes.^[3] Additionally, jade was used for adze heads, knives, and other weapons, which can be delicately shaped. As metal-working technologies became available, the beauty of jade made it valuable for ornaments and decorative objects. Jadeite measures between 6.0 and 7.0 Mohs hardness, and nephrite between 6.0 and 6.5, so it can be worked with quartz or garnet sand, and polished with bamboo or even ground jade.^{[citation needed]}

Unusual varieties

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Nephrite can be found in a creamy white form (known in China as "mutton fat" jade) as well as in a variety of green colours, whereas jadeite shows more colour variations, including blue, lavender-mauve, pink, and emerald-green colours. Of the two, jadeite is rarer, documented in fewer than 12 places worldwide. Translucent emerald-green jadeite is the most prized variety, both historically and today. As "quetzal" jade, bright green jadeite from Guatemala was treasured by Mesoamerican cultures, and as "kingfisher" jade, vivid green rocks from Burma became the preferred stone of post-1800 Chinese imperial scholars and rulers. Burma (Myanmar) and Guatemala are the principal sources of modern gem jadeite. In the area of Mogaung in the Myitkyina District of Upper Burma, jadeite formed a layer in the dark-green serpentine, and has been quarried and exported for well over a hundred years.^[4] Canada provides the major share of modern lapidary nephrite. Nephrite jade was used mostly in pre-1800 China as well as in New Zealand, the Pacific Coast and Atlantic Coasts of North America, Neolithic Europe, and Southeast Asia. In addition to Mesoamerica, jadeite was used by Neolithic Japanese and European cultures.

History

Prehistoric and historic China

Main article: Chinese jade

Jade dragon, Western Han Dynasty (202 BC – 9 AD)

Large "mutton fat" nephrite jade displayed in Hotan Cultural Museum lobby.

During Neolithic times, the key known sources of nephrite jade in China for utilitarian and ceremonial jade items were the now depleted deposits in the Ningshao area in the Yangtze River Delta (Liangzhu culture 3400–2250 BC) and in an area of the Liaoning province and Inner Mongolia (Hongshan culture 4700–2200 BC).^[5] Dushan Jade was being mined as early as 6000 BC. In the Yin Ruins of the Shang Dynasty (1600 to 1050 BC) in Anyang, Dushan Jade ornaments were unearthed in the tomb of the Shang kings. Jade was used to create many utilitarian and ceremonial objects, from indoor decorative items to jade burial suits. Jade was considered the "imperial gem". From the earliest Chinese dynasties to the present, the jade deposits most in use were not only those of Khotan in the Western Chinese province of Xinjiang but other parts of China as well, such as Lantian, Shaanxi. There, white and greenish nephrite jade is found in small quarries and as pebbles and boulders in the rivers flowing from the Kuen-Lun mountain range eastward into the Takla-Makan desert area. The river jade collection is concentrated in the Yarkand, the White Jades (Yurungkash) and Black Jade (Karakash) Rivers. From the Kingdom of Khotan, on the southern leg of the Silk Road, yearly tribute payments consisting of the most precious white jade were made to the Chinese Imperial court and there worked into objets d'art by skilled artisans as jade had a status-value exceeding that of gold or silver. Jade became a favourite material for the crafting of Chinese scholars' objects, such as rests for calligraphy brushes, as well as the mouthpieces of some opium pipes, due to the belief that breathing through jade would bestow longevity upon smokers who used such a pipe.^[6]
Jadeite, with its bright emerald-green, pink, lavender, orange and brown colours was imported from Burma to China only after about 1800. The vivid green variety became known as Feicui (翡翠) or Kingfisher (feathers) Jade. It quickly became almost as popular as nephrite and a favorite of Qing Dynasty's nouveau riche, while scholars still had strong attachment to nephrite (white jade, or Khotan), which they deemed to be the symbol of a nobleman.
In the history of the art of the Chinese empire, jade has had a special significance, comparable with that of gold and diamonds in the West.^[7] Jade was used for the finest objects and cult figures, and for grave furnishings for high-ranking members of the imperial family.^[7] Due to that significance and the rising middle class in China, today the finest jade when found in nuggets of “mutton fat” jade — so-named for its marbled white consistency — can fetch $3,000 an ounce, a tenfold increase from a decade ago.^[8]

Prehistoric and historic India

The Jainist temple of Kolanpak in the Nalgonda district, Andhra Pradesh, India is home to a 5-foot (1.5 m) high sculpture of Mahavira that is carved entirely out of jade. It is the largest sculpture made from a single jade rock in the world. India is also noted for its craftsman tradition of using large amounts of green serpentine or false jade obtained primarily from Afghanistan in order to fashion jewellery and ornamental items such as sword hilts and dagger handles.^[4]

Prehistoric and early historic Korea

Jadeite Pectoral from the Mayan Classic period (195 mm or 7.7 in high)

The use of jade and other greenstone was a long-term tradition in Korea (c. 850 BC – AD 668). Jade is found in small numbers of pit-houses and burials. The craft production of small comma-shaped and tubular "jades" using materials such as jade, microcline, jasper, etc., in southern Korea originates from the Middle Mumun Pottery Period (c. 850–550 BC).^[9] Comma-shaped jades are found on some of the gold crowns of Silla royalty (c. 300/400–668 AD) and sumptuous elite burials of the Korean Three Kingdoms. After the state of Silla united the Korean Peninsula in 668, the widespread popularisation of death rituals related to Buddhism resulted in the decline of the use of jade in burials as prestige mortuary goods.

Māori

Nephrite jade in New Zealand is known as pounamu in the Māori language (often called "greenstone" in New Zealand English), and plays an important role in Māori culture. It is considered a taonga, or treasure, and therefore protected under the Treaty of Waitangi, and the exploitation of it is restricted and closely monitored. It is found only in the South Island of New Zealand, known as Te Wai Pounamu in Māori—"The [land of] Greenstone Water", or Te Wahi Pounamu—"The Place of Greenstone".
Tools, weapons and ornaments were made of it; in particular adzes, the 'mere' (short club), and the Hei-tiki (neck pendant). These were believed to have their own mana, handed down as valuable heirlooms, and often given as gifts to seal important agreements. Nephrite jewellery of Maori design is widely popular with locals and tourists, although some of the jade used for these is now imported from British Columbia and elsewhere.^[10]

Canada

Mesoamerica

Main article: Jade use in Mesoamerica

Jade was a rare and valued material in pre-Columbian Mesoamerica. The only source from which the various indigenous cultures, such as the Olmec and Maya, could obtain jade was located in the Motagua River valley in Guatemala. Jade was largely an elite good, and was usually carved in various ways, whether serving as a medium upon which hieroglyphs were inscribed, or shaped into symbolic figurines. Generally, the material was highly symbolic, and it was often employed in the performance of ideological practices and rituals.

Enhancement

Jade may be enhanced (sometimes called "stabilized"). Note that some merchants will refer to these as Grades, but it is important to bear in mind that degree of enhancement is different from colour and texture quality. In other words, Type A jadeite is not enhanced but can have poor colour and texture. There are three main methods of enhancement, sometimes referred to as the ABC Treatment System:^[11]

• Type A jadeite has not been treated in any way except surface waxing.
• Type B treatment involves exposing a promising but stained piece of jadeite to chemical bleaches and/or acids and impregnating it with a clear polymer resin. This results in a significant improvement of transparency and colour of the material. Currently, infrared spectroscopy is the most accurate test for the detection of polymer in jadeite.
• Type C jade has been artificially stained or dyed. The effects are somewhat uncontrollable and may result in a dull brown. In any case, translucency is usually lost.
• B+C jade is a combination of B and C: it has been both impregnated and artificially stained.
• Type D jade refers to a composite stone such as a doublet comprising a jade top with a plastic backing.

See also

• Axstone
• Costa Rican jade tradition
• False Jade or Serpentine
• Heavenly Horse Tomb, a Silla royal tomb in Korea with jade artifacts.
• Jade burial suit
• Mumun Pottery Period, the time in Korea when jade ornament production began
• Pounamu

References

1. ^ "Online Etymology Dictionary". Etymonline.com. Retrieved 2011-03-07.
2. ^ Easby, Elizabeth Kennedy. Pre-Columbian Jade from Costa Rica. (1968). André Emmerich Inc., New York
3. ^ Liu, Li. The Products of Minds as Well as Hands: Production of Prestige Goods in Neolithic and Early State Periods of China. Asian Perspectives 42(1):1-40, 2003, pg 2.
4. ^ ^{a b} Hunter, Sir William Wilson and Burn, Sir Richard, The Imperial Gazeteer of India, Vol. 3, Oxford, England: Clarendon Press, Henry Frowde Publishers (1907), p. 242
5. ^ Liu, Li 2003:3-15
6. ^ Martin, Steven. The Art of Opium Antiques. Silkworm Books, Chiang Mai, 2007
7. ^ ^{a b} Jade. Gemstone.org
8. ^ Jacobs, Andrew (September 20, 2010). "Jade From China’s West Surpasses Gold in Value". The New York Times (New York: NYTC). ISSN 0362-4331. Retrieved October 13, 2012.
9. ^ Bale, Martin T. and Ko, Min-jung. Craft Production and Social Change in Mumun Pottery Period Korea. Asian Perspectives 45(2):159-187, 2006.
10. ^ Salt, Donn, 1992, Stone, Bone and Jade - 24 New Zealand Artists, David Bateman Ltd, Auckland.
11. ^ "Tay Thye Sun, The Changing Face of Jade" (PDF). Alumni Newsletter No. 3, pp. 5 - 6. Ssef-alumni.org.