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Beryl

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Beryl

"Beril" and "Heliodor" redirect here. For the character in Tolkien's legendarium, see House of Bëor. For the given names, see Beryl (given name) or Heliodorus (given name). For the Sailor Moon villain, see Queen Beryl. For other uses, see Beryl (disambiguation).
Beryl
Three varieties of beryl: morganite, aquamarine and heliodor
General
Category Cyclosilicate
Formula
(repeating unit)
Be3Al2Si6O18
Strunz classification 09.CJ.05
Crystal symmetry Hexagonal dihexagonal dipyramidal
H-M symbol (6/m 2/m 2/m)
Space group: P 6/mmc
Unit cell a = 9.21 Å, c = 9.19 Å; Z = 2
Identification
Formula mass 537.50
Color Green, blue, yellow, colorless, pink and others
Crystal habit Prismatic to tabular crystals; radial, columnar; granular to compact massive
Crystal system Hexagonal
Twinning Rare
Cleavage Imperfect on {0001}
Fracture Conchoidal to irregular
Tenacity Brittle
Mohs scale hardness 7.5–8
Luster Vitreous to resinous
Streak White
Diaphaneity Transparent to translucent
Specific gravity Average 2.76
Optical properties Uniaxial (-)
Refractive index nω = 1.564–1.595
nε = 1.568–1.602
Birefringence δ = 0.0040–0.0070
Pleochroism Weak to distinct
Ultraviolet fluorescence None (some fracture filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not). Morganite has weak violet fluorescence.
References [1][2][3][4]

In geology, beryl is a mineral composed of beryllium aluminium cyclosilicate with the chemical formula Be3Al2Si6O18. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red, and white.

Etymology

The name beryl is derived (via Latin: beryllus, Old French: beryl, and Middle English: beril) from Greek βήρυλλος beryllos which referred to a "precious blue-green color-of-sea-water stone"; akin to Prakrit verulia, veluriya ("beryl").[5] The German word Brille and the Dutch word bril (eyeglasses) are also derived from Prakrit verulia.[6] The term was later adopted for the mineral beryl more exclusively.[2]

Deposits

Beryl of various colors is found most commonly in Idaho, Maine, New Hampshire, North Carolina, South Dakota and Utah.

New England's pegmatites have produced some of the largest beryls found, including one massive crystal from the Bumpus Quarry in Albany, Maine with dimensions 5.5 by 1.2 m (18.0 by 3.9 ft) with a mass of around 18 metric tons; it is New Hampshire's state mineral. As of 1999, the world's largest known naturally occurring crystal of any mineral is a crystal of beryl from Malakialina, Madagascar, 18 m (59 ft) long and 3.5 m (11 ft) in diameter, and weighing 380,000 kg (840,000 lb).[7]

Varieties

Aquamarine and maxixe

Aquamarine
Faceted aquamarine, 13.24ct, Brazil

Aquamarine (from Latin: aqua marina, "water of the sea") is a blue or cyan variety of beryl. It occurs at most localities which yield ordinary beryl. The gem-gravel placer deposits of Sri Lanka contain aquamarine. Clear yellow beryl, such as that occurring in Brazil, is sometimes called aquamarine chrysolite. The deep blue version of aquamarine is called maxixe. Maxixe is commonly found in the country of Madagascar. Its color fades to white when exposed to sunlight or is subjected to heat treatment, though the color returns with irradiation.

The pale blue color of aquamarine is attributed to Fe2+. The Fe3+ ions produce golden-yellow color, and when both Fe2+ and Fe3+ are present, the color is a darker blue as in maxixe. Decoloration of maxixe by light or heat thus may be due to the charge transfer between Fe3+ and Fe2+.[8][9][10][11] Dark-blue maxixe color can be produced in green, pink or yellow beryl by irradiating it with high-energy particles (gamma rays, neutrons or even X-rays).[12]

In the United States, aquamarines can be found at the summit of Mt. Antero in the Sawatch Range in central Colorado. In Wyoming, aquamarine has been discovered in the Big Horn Mountains, near Powder River Pass. Another location within the United States is the Sawtooth Range near Stanley, Idaho. Although the minerals are within a wilderness area which prevents collecting. In Brazil, there are mines in the states of Minas Gerais, Espírito Santo, and Bahia, and minorly in Rio Grande do Norte. The mines of Colombia, Zambia, Madagascar, Malawi, Tanzania and Kenya also produce aquamarine.

The largest aquamarine of gemstone quality ever mined was found in Marambaia, Minas Gerais, Brazil, in 1910. It weighed over 110 kg (240 lb), and its dimensions were 48.5 cm (19 in) long and 42 cm (17 in) in diameter.[13] The largest cut aquamarine gem is the Dom Pedro aquamarine, now housed in the Smithsonian Institution's National Museum of Natural History.[14]

Emerald

Faceted emerald, 1.07ct, Colombia
Rough emerald on matrix

Emerald is green beryl, colored by trace amounts of chromium and sometimes vanadium.[8][15] The word "emerald" comes (via Middle English: Emeraude, imported from Old French: Ésmeraude and Medieval Latin: Esmaraldus) from Latin smaragdus from Greek smaragdos – σμάραγδος ("green gem"), its original source being a Semitic word izmargad (אזמרגד) or the Sanskrit word, marakata (मरकत), meaning "green".[16] Most emeralds are highly included, so their brittleness (resistance to breakage) is classified as generally poor.

Emeralds in antiquity were mined by the Egyptians and in Austria, as well as Swat in northern Pakistan.[17] A rare type of emerald known as a trapiche emerald is occasionally found in the mines of Colombia. A trapiche emerald exhibits a "star" pattern; it has raylike spokes of dark carbon impurities that give the emerald a six-pointed radial pattern. It is named for the trapiche, a grinding wheel used to process sugarcane in the region. Colombian emeralds are generally the most prized due to their transparency and fire. Some of the rarest emeralds come from three main emerald mining areas in Colombia: Muzo, Coscuez, and Chivor. Fine emeralds are also found in other countries, such as Zambia, Brazil, Zimbabwe, Madagascar, Pakistan, India, Afghanistan and Russia. In the US, emeralds can be found in Hiddenite, North Carolina. In 1998, emeralds were discovered in the Yukon.

Emerald is a rare and valuable gemstone and, as such, it has provided the incentive for developing synthetic emeralds. Both hydrothermal[18] and flux-growth synthetics have been produced. The first commercially successful emerald synthesis process was that of Carroll Chatham.[19] The other large producer of flux emeralds was Pierre Gilson Sr., which has been on the market since 1964. Gilson's emeralds are usually grown on natural colorless beryl seeds which become coated on both sides. Growth occurs at the rate of 1 mm per month, a typical seven-month growth run producing emerald crystals of 7 mm of thickness.[20] The green color of emeralds is widely attributed to presence of Cr3+ ions.[9][10][11] Intensely green beryls from Brazil, Zimbabwe and elsewhere in which the color is attributed to vanadium have also been sold and certified as emeralds.[21][22][23]

Golden beryl and heliodor

Faceted Heliodor, 48.75 ct, Brazil
Golden beryl
Heliodor

Golden beryl can range in colors from pale yellow to a brilliant gold. Unlike emerald, golden beryl has very few flaws. The term "golden beryl" is sometimes synonymous with heliodor (from Greek hēlios – ἥλιος "sun" + dōron – δῶρον "gift") but golden beryl refers to pure yellow or golden yellow shades, while heliodor refers to the greenish-yellow shades. The golden yellow color is attributed to Fe3+ ions.[8][9] Both golden beryl and heliodor are used as gems. Probably the largest cut golden beryl is the flawless 2054 carat stone on display in the Hall of Gems, Washington, D.C., United States.[24]

Goshenite

Faceted goshenite, 1.88 ct, Brazil
Goshenite

Colorless beryl is called goshenite. The name originates from Goshen, Massachusetts where it was originally discovered. Since all these color varieties are caused by impurities and pure beryl is colorless, it might be tempting to assume that goshenite is the purest variety of beryl. However, there are several elements that can act as inhibitors to color in beryl and so this assumption may not always be true. The name goshenite has been said to be on its way to extinction and yet it is still commonly used in the gemstone markets. Goshenite is found to some extent in almost all beryl localities. In the past, goshenite was used for manufacturing eyeglasses and lenses owing to its transparency. Nowadays, it is most commonly used for gemstone purposes and also considered as a source of beryllium.[25][26]

The gem value of goshenite is relatively low. However, goshenite can be colored yellow, green, pink, blue and in intermediate colors by irradiating it with high-energy particles. The resulting color depends on the content of Ca, Sc, Ti, V, Fe, and Co impurities.[9]

Morganite

Faceted morganite, 2.01ct, Brazil
Morganite

Morganite, also known as "pink beryl", "rose beryl", "pink emerald", and "cesian (or caesian) beryl", is a rare light pink to rose-colored [8]

Pink beryl of fine color and good sizes was first discovered on an island on the coast of Madagascar in 1910.[27] It was also known, with other gemstone minerals, such as [27]

On October 7, 1989, one of the largest gem morganite specimens ever uncovered, eventually called "The Rose of Maine," was found at the Bennett Quarry in Buckfield, Maine, US.[28] The crystal, originally somewhat orange in hue, was 23 cm (9 in) long and about 30 cm (12 in) across, and weighed (along with its matrix) just over 50 pounds (23 kg).[29]

Red beryl

Faceted red beryl, 0.56 ct, Utah US
Red beryl

Red beryl (also known as "red emerald" or "scarlet emerald") is a red variety of beryl. It was first described in 1904 for an occurrence, its type locality, at Maynard's Claim (Pismire Knolls), Thomas Range, Juab County, Utah.[30][31] The old synonym "bixbite" is deprecated from the CIBJO, because of the risk of confusion with the mineral bixbyite (also named after the mineralogist Maynard Bixby). The dark red color is attributed to Mn3+ ions.[8]

Red beryl is very rare and has only been reported from a handful of locations including: Wah Wah Mountains, Beaver County, Utah; Paramount Canyon and Round Mountain, Sierra County, New Mexico, although the latter locality does not often produce gem grade stones;[1] and Juab County, Utah. The greatest concentration of gem-grade red beryl comes from the Ruby-Violet Claim in the Wah Wah Mountains of the Thomas range of mid-western Utah, discovered in 1958 by Lamar Hodges, of Fillmore, Utah, while he was prospecting for uranium.[32] Red beryl has been known to be confused with pezzottaite, a caesium analog of beryl, that has been found in Madagascar and more recently Afghanistan – although cut gems of the two varieties can be distinguished from their difference in refractive index, and rough crystals can be easily distinguished by differing crystal systems (pezzottaite trigonal, red beryl hexagonal). Synthetic red beryl is also produced.[33]

While gem beryls are ordinarily found in pegmatites and certain metamorphic stones, red beryl occurs in topaz-bearing rhyolites. It is formed by crystallizing under low pressure and high temperature from a pneumatolytic phase along fractures or within near-surface miarolitic cavities of the rhyolite. Associated minerals include bixbyite, quartz, orthoclase, topaz, spessartine, pseudobrookite and hematite.[34]

See also

References

  1. ^ a b Beryl mineral information and data, Mindat
  2. ^ a b Beryl Webmineral
  3. ^ Handbook of Mineralogy
  4. ^ Schumann, Walter, 2013, Gemstones of the World, 5th ed., ISBN 1-454-90953-6
  5. ^
  6. ^ Olivelle, Patrick (2006), Between the Empires, Society in India 300 BCE to 400 CE, page 463, Oxford University Press.
  7. ^ G. Cressey and I. F. Mercer, (1999) Crystals, London, Natural History Museum, page 58
  8. ^ a b c d e
  9. ^ a b c d
  10. ^ a b
  11. ^ a b
  12. ^
  13. ^
  14. ^
  15. ^
  16. ^
  17. ^
  18. ^
  19. ^ Gemology Project
  20. ^ Nassau, K., 1980, Gems Made By Man, Gemological Institute of America, ISBN 0-87311-016-1
  21. ^
  22. ^
  23. ^
  24. ^
  25. ^
  26. ^
  27. ^ a b
  28. ^
  29. ^ The Rose of Maine, image, The Rose of Maine at the site of its discovery
  30. ^ MinDat – Red beryl
  31. ^ Carl Ege, Utah Geological Survey
  32. ^
  33. ^ "Bixbite" – The Gemstone List
  34. ^
  • Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7
  • Sinkankas, John, 1994, Emerald & Other Beryls, Geoscience Press, ISBN 0-8019-7114-4

External links

  • The dictionary definition of beryl at Wiktionary
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