Topaz is a silicate mineral made of aluminum and fluorine with the chemical formulaAl2SiO4(F, OH)2. It is used as a gemstone in jewelry and other adornments. Common topaz in its natural state is colorless, though trace element impurities can make it pale blue or golden brown to yellow-orange.[7] Topaz is often treated with heat or radiation to make it a deep blue, reddish-orange, pale green, pink, or purple.[8]
It occurs in many places in the world. Some of the most popular places where topaz is sourced are Brazil and Russia.[7] Topaz is often mined in open pit or alluvial settings.[11]
Etymology
The word "topaz" is usually believed to be derived (via Old French: Topace and Latin: Topazius) from the GreekΤοπάζιος (Topázios) or Τοπάζιον (Topázion),[12] from Τοπαζος. This is the ancient name of St. John's Island in the Red Sea which was difficult to find and from which a yellow stone (now believed to be chrysolite: yellowish olivine) was mined in ancient times. The name topaz was first applied to the mineral now known by that name in 1737.[13] Ancient Sri Lanka (Tamraparni) exported topazes to Greece and ancient Egypt, which led to the etymologically related names of the island by Alexander Polyhistor (Topazius) and the early Egyptians (Topapwene) – "land of the Topaz".[14][15]Pliny said that Topazos is a legendary island in the Red Sea and the mineral "topaz" was first mined there. Alternatively, the word topaz may be related to the Sanskrit word तपस् "tapas", meaning "heat" or "fire".[12]
History
Nicols, the author of one of the first systematic treatises on minerals and gemstones, dedicated two chapters to the topic in 1652.[16] In the Middle Ages, the name topaz was used to refer to any yellow gemstone, but in modern times it denotes only the silicate described above.
Many English translations of the Bible, including the King James Version, mention topaz. However, because these translations as topaz all derive from the Septuagint translation topazi[os], which referred to a yellow stone that was not topaz, but probably chrysolite (chrysoberyl or peridot), topaz is likely not meant here.[17]
An English superstition also held that topaz cured lunacy.[18] The ancient Romans believed that topaz provided protection from danger while traveling.[19] During the Middle Ages, it was believed that attaching the topaz to the left arm protected the owner from any curse and warded off the evil eye. It was also believed that wearing topaz increased body heat, which would enable people to relieve a cold or fever.[20] In Europe during the Middle Ages, topaz was believed to enhance mental powers.[21] In India, people believed topaz granted beauty, intelligence, and longevity when worn over the heart.[22]
Gemstone
Topaz is a gemstone. In cut and polished form, it is used to make jewelry or other adornments. Lower quality topaz is commonly used as an abrasive material due to its hardness and it is used to produce refractory materials for high temperature environments.[7] Topaz can be used as a flux in steel production.[23] Using topaz as a refectory material does have some health and environmental concerns due to the production of fluorine as a byproduct of calcining topaz.
Orange topaz, also known as precious topaz, is the birthstone for the month of November, the symbol of friendship, and the state gemstone of the U.S. state of Utah.[24] Blue topaz is the state gemstone of the US state of Texas.[25] The 4th wedding anniversary gem is blue topaz and the 23rd is imperial topaz.[22]
Synthetic topaz can be produced using a method that includes the thermal hydrolysis of SiO2 and AlF3.[26] When these compounds are heated to temperatures of 750° to 850°C topaz is formed. Another method uses a combination of amorphous Al2O3, Na2SiF6, and water which is heated to a temperature of 500°C, put under a pressure of 4000 bars, and left for 9 days.[26]
To care for a topaz gemstone, it is best to avoid ultrasonic cleaners or steam as this could produce small fractures within the crystal.[22] Warm water with soap is the best way to wash it.
To choose an ethically sourced topaz gemstone, it is recommended to search for a stone that the seller knows the origin of.[27] If the seller cannot produce information about the locality and mine that the topaz was collected from, it is likely that it was collected unethically.
Mineralogy
Topaz's crystal structure using polyhedrons showcasing the aluminum octahedron (grey), silica tetrahedron (blue), oxygen (red), and fluorine (green).
Topaz is an accessory mineral to felsic igneous, sedimentary, and hydrothermally altered rocks.[28]
The crystal structure of topaz alternates between sheets of (F, OH)2O and O along (010) with Al3+ occupying the octahedral sites and Si4+ in the tetrahedral sites.[28] Fluorine can be substituted by hydroxide in topaz by up to 30mol.% in nature and hydroxide-dominating topaz can be made in laboratories but has not been found in nature.[29]
On occasion, cavities can be found within topaz and they are filled with a liquid called brewsterlinite.[26] Brewsterlinite was discovered by David Brewster upon heating a sample of topaz.[30] After heating, the topaz lost mass, and through examination Brewster concluded Topaz was formed in a wet environment creating these liquid-filled cavities. This liquid is a hydrocarbon with a refractive index of 1·13.[26]
Topaz's crystal habit takes many forms. It can display a range of slender and long crystals to bulky and short.[29] There can also be variation in the terminations displaying blunt, pyramidal, chisel, or wedge-shaped terminations. The perfect cleavage {001} in topaz breaks no Si-O bonds within its structure and only breaks Al-O and Al-F bonds.[31] This cleavage is diagnostic for this mineral. The 2V optical angle in topaz can range from 48° to 69.5°.[29] Low fluorine content yields a smaller angle and high fluorine content yields a larger angle.
Characteristics
Blue topaz crystal
Topaz in its natural state is colorless, often with a greyish cast. It also occurs as a golden brown to yellow color which makes it sometimes confused with citrine, a less valuable gemstone.[32] The specific gravity of all shades of topaz, however, means that it is considerably heavier than citrine (about 25% per volume) and this difference in weight can be used to distinguish two stones of equal volume. Also, if the volume of a given stone can be determined, its weight if it were topaz can be established and then checked with a sensitive scale. Likewise, glass stones are also much lighter than equally sized topaz.
A variety of impurities and treatments may make topaz wine red, pale gray, reddish-orange, pale green, or pink (rare), and opaque to translucent/transparent. The pink and red varieties come from chromium replacing aluminium in its crystalline structure.[33]
Large topaz gemstone and small irradiated topaz fragment on display at the Smithsonian Museum of Natural History.
Imperial topaz is yellow, pink (rare, if natural), or pink-orange. Brazilian imperial topaz can often have a bright yellow to deep golden brown hue, sometimes even violet. Many brown or pale topazes are treated to make them bright yellow, gold, pink, or violet colored. Some imperial topaz stones can fade from exposure to sunlight for an extended period of time.[34][35] Naturally occurring blue topaz is quite rare. Typically, colorless, gray, or pale yellow and blue material is heat treated and irradiated to produce a more desired darker blue.[35] Mystic topaz is a colorless topaz that has been artificially coated via a vapor deposition process giving it a rainbow effect on its surface.[36]
Sherry-colored topaz from Utah, USA
Although very hard, topaz must be treated with greater care than some other minerals of similar hardness (such as corundum) because of a weakness of atomic bonding of the stone's molecules along one or another axial plane (whereas diamonds, for example, are composed of carbon atoms bonded to each other with equal strength along all of its planes). This gives topaz a tendency to break along such a cleavage plane if struck with sufficient force.[37]
Topaz has a relatively low index of refraction for a gemstone, and so stones with large facets or tables do not sparkle as readily as stones cut from minerals with higher refractive indices, though quality colorless topaz sparkles and shows more "life" than similarly cut quartz. When given a typical "brilliant" cut, topaz may either show a sparkling table facet surrounded by dead-looking crown facets or a ring of sparkling crown facets with a dull well-like table.[38] It also takes an exceptionally fine polish, and can sometimes be distinguished from citrine by its slippery feel alone (quartz cannot be polished to this level of smoothness).[39]
Another method of distinguishing topaz from quartz is by placing the unset stone in a solution of bromoform or methylene iodide. Quartz will invariably float in these solutions, whereas topaz will sink.[39]
Localities and occurrence
Main topaz producing countries
Topaz is commonly associated with silicic igneous rocks of the granite and rhyolite type. It typically crystallizes in granitic pegmatites[7] or in vapor cavities in rhyolite lava flows including those at Topaz Mountain in western Utah and Chivinar in South America. It can be found with fluorite and cassiterite in various areas including the Ural and Ilmensky mountains of Russia, Afghanistan, Sri Lanka, the Czech Republic, Germany, Norway, Pakistan, Italy, Sweden, Japan, Brazil, Mexico; Flinders Island, Australia; Nigeria and the United States. Topaz was found around the time of the 1700s in a pegmatite formation within the central Urals Mountains in Russia.[7]
Topaz varieties found in Pakistan.
Brazil is one of the largest producers of topaz,[40] some clear topaz crystals from Brazilian pegmatites can reach boulder size and weigh hundreds of pounds. The Topaz of Aurangzeb, observed by Jean Baptiste Tavernier weighed 157.75 carats (31.550g).[41] The American Golden Topaz, a more recent gem, weighed 22,892.5 carats (4,578.50g). Large, vivid blue topaz specimens from the St. Anns mine in Zimbabwe were found in the late 1980s.[42] Colorless and light-blue varieties of topaz are found in Precambrian granite in Mason County, Texas[43] within the Llano Uplift. There is no commercial mining of topaz in that area.[44] It is possible to synthesize topaz.[45]
Mining
Large-scale topaz mining typically uses open pit and underground mining to extract the gem.[46] The waste material is discarded using large machines to transport it away while the valuable ore is washed and sorted to recover the topaz gems. In smaller-scale mines, dry sieving is used in alluvial environments by shoveling the material into sieves to separate the gems from unwanted dust and debris.[46] The topaz can then be selected by hand from the remaining material. Mined topaz is then sent to be processed for use in jewelry by polishing the gem and treating it to achieve the desired color.[46]
Mining for topaz can cause some environmental concerns mostly associated with larger-scale operations.[11] The introduction of a large open pit mine into an environment leads to modification of the land around it to make it accessible to workers. When the mine is done being used, they are often refilled with loose sediments left over from the mining process.[47] These loose sediments can be washed away to other areas and cut off water features, destroy farmland, and create a threat of landslides. The pollution produced by mining can impact the environment around it and damage its health.[47]Deforestation undergone to create the mine along with the machinery used during the mining process add greenhouse gasses to the atmosphere. Deforestation also removes habitats and biodiversity from a large area of natural space. This disruption to the ecosystem can be challenging to the wildlife and local populations. Water is also a large component of mining operations which draws it away from neighbouring communities and creates a lack of water.[11]Tailings leftover from the mining process can leach contaminants into nearby water systems which can get into the drinking water of local communities.[47]
Some ways humans can be impacted by gem mining is through danger in mines and inadequate compensation.[47] Accidents such as collapsing mines and machinery malfunctioning can put human life in danger. Those working in the mines can also be exposed to harmful chemicals and heavy metals that can impact their health. For income, there can be an unequal dispersal of the funds made from gem mining between land owners, laborers, and the operators of the mine. In illegal mining operations, there can be more money given to miners, however, these operations have fewer regulations and more dangerous environments.[47]
Beryl ( BERR-əl) is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, pink, and red (the rarest). It is an ore source of beryllium.
Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale. Most emeralds have much material trapped inside during the gem's formation, so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.
A gemstone is a piece of mineral crystal which, when cut or polished, is used to make jewelry or other adornments. Certain rocks and occasionally organic materials that are not minerals may also be used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some softer minerals such as brazilianite may be used in jewelry because of their color or luster or other physical properties that have aesthetic value. However, generally speaking, soft minerals are not typically used as gemstones by virtue of their brittleness and lack of durability.
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is, therefore, classified structurally as a framework silicate mineral and compositionally as an oxide mineral. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.
Tourmaline is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a wide variety of colors.
Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.
The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula BeAl2O4. The name chrysoberyl is derived from the Greek words χρυσός chrysos and βήρυλλος beryllos, meaning "a gold-white spar". Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones, although they both contain beryllium. Chrysoberyl is the third-hardest frequently encountered natural gemstone and lies at 8.5 on the Mohs scale of mineral hardness, between corundum (9) and topaz (8).
Zircon is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is ZrSiO4. An empirical formula showing some of the range of substitution in zircon is (Zr1–y, REEy)(SiO4)1–x(OH)4x–y. Zircon precipitates from silicate melts and has relatively high concentrations of high field strength incompatible elements. For example, hafnium is almost always present in quantities ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal system. The natural color of zircon varies between colorless, yellow-golden, red, brown, blue, and green.
Cubic zirconia (abbreviated CZ) is the cubic crystalline form of zirconium dioxide (ZrO2). The synthesized material is hard and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate (ZrSiO4). It is sometimes erroneously called cubic zirconium.
Pleochroism is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light.
Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate, LiAl(SiO3)2, and is a commercially important source of lithium. It occurs as colorless to yellowish, purplish, or lilac kunzite (see below), yellowish-green or emerald-green hiddenite, prismatic crystals, often of great size. Single crystals of 14.3 m (47 ft) in size are reported from the Black Hills of South Dakota, United States.
Tanzanite is the blue and violet variety of the mineral zoisite, caused by small amounts of vanadium. Tanzanite belongs to the epidote mineral group. Tanzanite is only found in Simanjiro District of Manyara Region in Tanzania, in a very small mining area approximately 7 km (4.3 mi) long and 2 km (1.2 mi) wide near the Mererani Hills.
Rhodochrosite is a manganese carbonate mineral with chemical composition MnCO3. In its pure form (rare), it is typically a rose-red colour, but it can also be shades of pink to pale brown. It streaks white, and its Mohs hardness varies between 3.5 and 4.5. Its specific gravity is between 3.45 and 3.6. The crystal system of rhodochrosite is trigonal, with a structure and cleavage in the carbonate rhombohedral system. The carbonate ions (CO2− 3) are arranged in a triangular planar configuration, and the manganese ions (Mn2+) are surrounded by six oxygen ions in an octahedral arrangement. The MnO6 octahedra and CO3 triangles are linked together to form a three-dimensional structure. Crystal twinning is often present. It can be confused with the manganese silicate rhodonite, but is distinctly softer. Rhodochrosite is formed by the oxidation of manganese ore, and is found in South Africa, China, and the Americas. It is one of the national symbols of Argentina.
Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten (wolfram). Scheelite is originally named after Swedish chemist Carl Wilhelm Scheele (1742–1786). Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. Scheelite has been synthesized using the Czochralski process; the material produced may be used to imitate diamond, as a scintillator, or as a solid-state lasing medium. It was also used in radium paint in the same fashion as was zinc sulphide, and Thomas Edison invented a fluoroscope with a calcium tungstate-coated screen, making the images six times brighter than those with barium platinocyanide; the latter chemical allowed Röntgen to discover X-rays in early November 1895. Note, the semi-precious stone marketed as 'blue scheelite' is actually a rock type consisting mostly of calcite and dolomite, with occasional traces of yellow-orange scheelite.
Brazilianite, whose name derives from its country of origin, Brazil, is a typically yellow-green phosphate mineral, most commonly found in phosphate-rich pegmatites.
Phenakite or phenacite is a fairly rare nesosilicate mineral consisting of beryllium orthosilicate, Be2SiO4. Occasionally used as a gemstone, phenakite occurs as isolated crystals, which are rhombohedral with parallel-faced hemihedrism, and are either lenticular or prismatic in habit: the lenticular habit is determined by the development of faces of several obtuse rhombohedra and the absence of prism faces. There is no cleavage, and the fracture is conchoidal. The Mohs hardness is high, being 7.5–8; the specific gravity is 2.96. The crystals are sometimes perfectly colorless and transparent, but more often they are greyish or yellowish and only translucent; occasionally they are pale rose-red. In general appearance the mineral is not unlike quartz, for which indeed it has been mistaken. Its name comes from Ancient Greek: φέναξ, romanized: phénax, meaning "deceiver" due to its close visual similarity to quartz, named by Nils Gustaf Nordenskiöld in 1833.
A diamond simulant, diamond imitation or imitation diamond is an object or material with gemological characteristics similar to those of a diamond. Simulants are distinct from synthetic diamonds, which are actual diamonds exhibiting the same material properties as natural diamonds. Enhanced diamonds are also excluded from this definition. A diamond simulant may be artificial, natural, or in some cases a combination thereof. While their material properties depart markedly from those of diamond, simulants have certain desired characteristics—such as dispersion and hardness—which lend themselves to imitation. Trained gemologists with appropriate equipment are able to distinguish natural and synthetic diamonds from all diamond simulants, primarily by visual inspection.
Jeremejevite is an aluminium borate mineral with variable fluoride and hydroxide ions. Its chemical formula is Al6B5O15(F,OH)3. It is considered as one of the rarest, thus one of the most expensive stones. For nearly a century, it was considered as one of the rarest gemstones in the world.
Chiolite is a tetragonal-ditetragonal dipyramidal mineral, composed of sodium, fluorine, and aluminium. The name originates from the combination of the Greek words for snow (χιώυ) and stone (λίθος). It is an allusion to its similarity and appearance to cryolite. Chiolite is an IMA approved mineral that has been grandfathered, meaning the name chiolite is believed to refer to a valid species to this day. Synonyms of chiolite are arksudite, arksutite, chodneffite, chodnewite and nipholith. It was first discovered in the Ilmen mountains, Russia, in 1846. Chiolite has been a valid species from the same year of its discovery.
Aquamarine is a pale-blue to light-green variety of the beryl family, with its name relating to water and sea. The color of aquamarine can be changed by heat, with a goal to enhance its physical appearance. It is the birth stone of March.
↑ Nesse, William D. (2000). Introduction to mineralogy. New York: Oxford University Press. p.313. ISBN9780195106916.
↑ Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20ed.). Wiley. ISBN0-471-80580-7.
↑ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (1995). "Topaz"(PDF). Handbook of Mineralogy. Vol.II (Silica, Silicates). Chantilly, VA, US: Mineralogical Society of America. ISBN978-0-9622097-1-0. Retrieved December 5, 2011.
1 2 3 4 Deer, W. A.; Howie, Robert A.; Zussman, Jack (1989). An introduction to the rock-forming minerals (16. impred.). London: Longman [u.a.] ISBN978-0-582-44210-8.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
