Beryl
| Beryl | |
 Three varieties of beryl: morganite, aquamarine, and heliodor | |
| General | |
|---|---|
| Category | Silicate mineral |
| Chemical formula | Be3Al2(SiO3)6 |
| Identification | |
| Molar mass | 537.50 |
| Color | Green, Blue, Yellow, Colorless, Pink & others. |
| Crystal habit | Massive to well Crystalline |
| Crystal system | Hexagonal (6/m 2/m 2/m) Space Group: P 6/mсc |
| Cleavage | Imperfect on the [0001] |
| Fracture | Conchoidal |
| Mohs Scalehardness | 7.5-8 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to opaque |
| 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 |
| Ultravioletfluorescence | None (some fracture filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not) |
The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formulaBe3Al2(SiO3)6. 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. The name comes from the Greek beryllos which referred to a precious blue-green color-of-sea-water stone.[1]The term was later adopted for the mineral beryl more exclusively.[2]
Deposits
Beryl of various colors is found most commonly in granitic pegmatites, but also occurs in micaschists in the Ural Mountains, and limestone in Colombia. Beryl is often associated with tinand tungsten ore bodies. Beryl is found in Europe in Norway, Austria, Germany, and Ireland, as well as Brazil, Colombia, Madagascar, Sweden (especially morganite), Russia, South Africa, the United States, and Zambia. U.S. beryl locations are in California, Colorado, Idaho,Maine, Connecticut, New Hampshire, North Carolina, South Dakota, and Utah.
The most famous source of emeralds in the world is at Muzo and Chivor, Boyacá, Colombia, where they make a unique appearance in limestone. Emerald are also found in the Transvaal, South Africa; Minas Gerais, Brazil; Zambia, and near Mursinka in the Ural Mountains in Russia. In the United States, emeralds are found in North Carolina.
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 m by 1.2 m (18 ft by 4 ft) with a mass of around 18 metric tons; it is New Hampshire's state mineral. As of 1999, the largest known crystal of any mineral in the world is a crystal of beryl from Madagascar, 18 meters long and 3.5 meters in diameter.[3]
Varieties
Varieties of beryl have been considered gemstones since prehistoric times:
Morganite
Morganite, also known as "pink beryl," "rose beryl," "pink emerald," and "cesian beryl," is a rare light pink to rose-colored gem-quality variety of beryl. Orange/yellow varieties of morganite can also be found, and color banding is common. It can be routinely heat treated to remove patches of yellow and is occasionally treated by irradiation to improve its color. The pink color of morganite is attributed to Mn2+ ions.[4]
Discovery and naming
Morganite was first discovered together with other gemstone minerals, such as tourmaline andkunzite, at Pala, California, early in the twentieth century. This started a bonanza for these quite popular gemstones which drew the attention of gemologist George Frederick Kunz, who knew that pink beryl was quite a rarity. [5] In 1911, Kunz suggested naming the pink variety of beryl "morganite" after financier J. P. Morgan.[6]
The Rose of Maine
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.[7] The crystal, originally somewhat orange in hue, was 23 cm long and about 30 cm across, and weighed (along with its matrix) just over 50 lbs (23 kg).[8]
Bixbite
Red beryl (also known as "bixbite", "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, USA.[9][10] 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 of bixbite is attributed to Mn3+ ions.[4]
Red beryl is rare and has only been reported from a handful of locations including: Wah Wah Mountains, Beaver County, Utah; Paramount Canyon,Sierra County, New Mexico; Round Mountain, Sierra County, New Mexico; and Juab County, Utah. The greatest concentration of gem-grade red beryl comes from the Violet Claim in the Wah Wah Mountains of mid-western Utah, discovered in 1958 by Lamar Hodges, of Fillmore, Utah, while he was prospecting for uranium.[11]
While gem beryls are ordinarily found in pegmatites and certain metamorphic rocks, bixbite occurs in topaz-bearing rhyolites. It formed by crystallizing under low pressure and high temperature from a pneumatolitic phase along fractures or within near-surface miarolitic cavities of the rhyolite. Associated minerals include bixbyite, quartz, orthoclase, topaz,spessartine, pseudobrookite and hematite. The red color is thought to be from manganesesubstituting for aluminium in the beryl structure.
Aquamarine and maxixe
Aquamarine (from Lat. aqua marina, "water of the sea") is a blue or turquoisevariety of beryl. It occurs at most localities which yield ordinary beryl, some of the finest coming from Russia. The gem-gravel placer deposits of Sri Lanka contain aquamarine. Clear yellow beryl, such as occurs in Brazil, is sometimes called aquamarine chrysolite. When corundum presents the bluish tint of typical aquamarine, it is often termed Oriental aquamarine. The deep blue version of aquamarine is called maxixe. 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 Fe3+ and Fe2+.[4][12][13][14] 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).[15]
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. In Brazil, there are mines in the states of Minas Gerais,Espírito Santo and Bahia. The Mines of Colombia, Zambia, Madagascar, Malawi, Tanzaniaand Kenya also produce aquamarine.
The biggest aquamarine ever mined was found at the city of Marambaia, Minas Gerais, Brazil, in 1910. It weighed over 110 kg, and its dimensions were 48.5 cm long and 42 cm in diameter.
Culture usage
- Aquamarine is the birthstone associated with March. It is also the gemstone for the 19th Anniversary.[citation needed]
Emerald
Emerald refers to green beryl, colored by trace amounts of chromium and sometimes vanadium.[4][16] The word "emerald" comes from Latinsmaragdus, its original source being a Semitic word izmargad or theSanskrit word, marakata, meaning "green".[17] Most emeralds are highlyincluded, 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 northernPakistan.[18] 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 thetrapiche, 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 most rare 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[19] and flux-growth synthetics have been produced. The first commercially successful emerald synthesis process was that of Carroll Chatham. 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 attributed to presense of Fe3+ and Fe2+ ions.[12] [13][14]
Goshenite
Colorless beryl is called goshenite. The name originates from Goshen, Massachusetts where it was originally described. 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. [21][22]
The gem value of gohenite is relatively low. However, goshenite can be colored yellow, green, pink, blue and in intermediate colors by irradiating it with high-energy particles. The resoluting color depends on the content of Ca, Sc, Ti, V, Fe, and Co inmpurities.[12]
Golden beryl and 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 helios "sun"), 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.[4][12] Both golden beryl and heliodor are used as gems. Probably the largest cut golden beryl is the flawless 2054 carat stone on display on display in the Hall of Gems,Washington, D.C.[23]
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