Chrysoberyl
General
Category	Mineral
Chemical formula	Beryllium aluminium oxide, BeAl2O4
Identification
Color	Various shades of green and yellow; brownish, reddish; rarely, blue
Crystal habit	slender prisms and tabular form, dimensions are thin in one direction. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 WikipediaNaming An oxide is a Chemical compound containing at least one Oxygen atom as well as at least one other element In Mineralogy, shape and size give rise to descriptive terms applied to the typical appearance or habit of Crystals The many terms used by mineralogists
Crystal system	Orthorhombic 2/m2/m2/m
Twinning	Contact and penetration twins common, often repeated forming rosette structures
Cleavage	[110] Distinct, [010] Imperfect
Fracture	Conchoidal to uneven
Mohs Scale hardness	8. A crystal system is a category of Space groups which characterize Symmetry of structures in three dimensions with Translational symmetry in three directions In Crystallography, the orthorhombic Crystal system is one of the seven Lattice Point groups Orthorhombic lattices result from stretching Crystal twinning occurs when two separate crystals share some of the same Crystal lattice points in a symmetrical manner Cleavage, in Mineralogy, is the tendency of crystalline materials to split along definite planes creating smooth surfaces of which there are several named types In the field of Mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a Mineral is broken The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material 5
Luster	Vitreous
Refractive index	Biaxial (+) nα=1. Lustre (or luster) is a description of the way light interacts with the surface of a Crystal, rock, or Mineral. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium 745 nβ=1. 748 nγ=1. 754
Pleochroism	Strong in alexandrite
Streak	White
Specific gravity	3. Pleochroism is an Optical phenomenon in which grains of a rock appear to be different colors when observed at different angles under a Petrographic microscope. The streak (also called powder color) of a Mineral is the Color of the powder produced when it is dragged across an unweathered surface Specific gravity is defined as the ratio of the Density of a given solid or liquid substance to the density of water at a specific temperature and pressure typically 5 - 3. 84
Major varieties
Alexandrite	Color change; green to red
Cymophane	Chatoyant

The mineral or gemstone chrysoberyl, not to be confused with beryl, is an aluminate of beryllium with the formula BeAl₂O₄. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash The Mineral beryl is a Beryllium Aluminium cyclosilicate with the Chemical formula Be3Al2(SiO36 WikipediaNaming Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 ^[1] The name chrysoberyl is derived from the Greek words chrysos and beryllos, meaning "a gold-white spar". Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones. Chrysoberyl is the fourth-hardest natural gemstone and lies between corundum and topaz on the hardness scale. Corundum (from Tamil kurundam குருந்தம் or kuruvindam குருவிந்தம் is a Crystalline form of Topaz is a Silicate mineral of Aluminium and Fluorine with the Chemical formula Al 2 Si[[oxygen O]]4( The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material Chrysoberyl is a mineral consisting of ordinary colorless or yellow transparent chrysoberyl, cymophane (chrysoberyl cat's eye), and alexandrite. ^[2]

An interesting feature of its crystals are the cyclic twins called trillings. Crystal twinning occurs when two separate crystals share some of the same Crystal lattice points in a symmetrical manner These twinned crystals have a hexagonal appearance, but are the result of a triplet of twins with each "twin" taking up 120 degrees of the cyclic trilling.

There are three main varieties of chrysoberyl: ordinary yellow chrysoberyl, cat's eye or cymophane, and alexandrite. Although yellow chrysoberyl was referred to as chrysolite during the Victorian and Edwardian eras, that name is no longer used in the gemological nomenclature.

Ordinary chrysoberyl is a yellowish-green, transparent to translucent chrysoberyl and has often been referred to in the literature as chrysolite due to the common olive color of many of its gems, but that name is no longer used in the gemological nomenclature. When the mineral exhibits good pale green to yellow color and is transparent, then it is used as a gemstone.

Alexandrite, a strongly pleochroic (trichroic) gem, will exhibit emerald green, red and orange-yellow colors and tend to change color in artificial light compared to daylight. Pleochroism is an Optical phenomenon in which grains of a rock appear to be different colors when observed at different angles under a Petrographic microscope. The color change from red to green is due to strong absorption of light in the yellow and blue portions of the spectrum. Typically, alexandrite has an emerald-green color in daylight but exhibit a raspberry-red color in incandescent light.

Cymophane is popularly known as cat's eye. This variety exhibits pleasing chatoyant or opalescence that reminds one of an eye of a cat. In Gemology, chatoyancy (or chatoyance) is an optical reflectance effect seen in certain Gemstones Coined from the French "oeil de chat" When cut to produce a cabochon, the mineral forms a light-green specimen with a silky band of light extending across the surface of the stone.

Occurrence

Chrysoberyl was formed as a result of pegmatitic processes. High temperatures and pressures from the outer layers of the earth's mantle forced molten magma towards the surface. As the main magma body cooled, water originally present in low concentrations became more concentrated in the molten rock because it could not be incorporated into the crystallization of the localized minerals. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet Crystallization is the (natural or artificial process of formation of solid Crystals precipitating from a homogeneous --> identical Solution Consequently, the remaining portion of the molten magma was water-rich. It was also rich in rare elements and silica that still had not solidified. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide When this water-rich magma was expelled in the final stages of the crystallization, it solidified in cracks and crevasses to form a pegmatite. Pegmatite is a very coarse-grained Igneous rock that has a grain size of 20 mm or more such rocks are referred to as pegmatitic.

If the pegmatite magma was rich in beryllium, crystals of beryl and chrysoberyl could form but for alexandrite to form, some chromium would also have had to be present. Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 The Mineral beryl is a Beryllium Aluminium cyclosilicate with the Chemical formula Be3Al2(SiO36 Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 Since beryllium and chromium are extremely rare elements in rocks, this is the only known process which could have concentrated these unusual elements in an environment where crystallization could occur.

The high water content of the magma made it possible for the crystals to grow quickly, so pegmatite crystals are often quite large and this is of course important for gem specimens. Chrysoberyl is always accompanied by quartz. It occurs in granite pegmatites and mica schists and in contact with metamorphic deposits of dolomitic marble. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially The schists form a group of medium-grade Metamorphic rocks chiefly notable for the preponderance of lamellar Minerals such as Micas chlorite Dolomite (ˈdɒləmaɪt is the name of a Sedimentary Carbonate rock and a Mineral, both composed It is also recovered from river sands and gravels in alluvial deposits with corundum, spinel, garnet, and tourmaline. Corundum (from Tamil kurundam குருந்தம் or kuruvindam குருவிந்தம் is a Crystalline form of The spinels are any of a class of Minerals of general formulation XY2 O 4 which Crystallize in the cubic (isometric The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives Tourmaline is a Crystal Silicate mineral compounded with elements such as Aluminium, Iron, Magnesium, Sodium, Lithium

Chrysoberyl has high-enough specific gravity that it will concentrate with black sands in active or paleoplacer stream deposits and concentrate with other relatively heavy minerals such as cassiterite, diamond, corundum, topaz, and garnet. Cassiterite is a Tin Oxide Mineral, SnO2. It is generally opaque but is translucent in thin crystals In Mineralogy, diamond is the allotrope of carbon where the carbon atoms are arranged in Corundum (from Tamil kurundam குருந்தம் or kuruvindam குருவிந்தம் is a Crystalline form of Topaz is a Silicate mineral of Aluminium and Fluorine with the Chemical formula Al 2 Si[[oxygen O]]4( The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives When found in placers, it will have rounded edges instead of sharp, wedge-shape forms. In Geology, a placer deposit or placer is an accumulation of valuable minerals formed by deposition of dense mineral phases in a trap site Much of the chrysoberyl mined in Brazil and Sri Lanka is recovered from placers as the host rocks have been intensely weathered and eroded. |utc_offset = -2 to -4 |time_zone_DST = BRST |utc_offset_DST = -2 to -5 |cctld Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka ( Sinhalese:, இலங்கை known as Ceylon before 1972 is an Island

Chrysoberyl deposits can be divided into three types, excluding rare dolomitic hosts. Dolomite (ˈdɒləmaɪt is the name of a Sedimentary Carbonate rock and a Mineral, both composed These include chrysoberyl in pegmatites intruded into ultramafic rocks, chrysoberyl hosted by pegmatites intruded into aluminous rocks, and chrysoberyl found as a primary mineral in REE-pegmatites.

There have been very few research projects on the genesis of chrysoberyl due to its rarity in primary host rocks since most chrysoberyl is recovered from placers. However, it may be hypothesized that in order to produce chrysoberyl, metamorphic overprint of some beryllium- and aluminum-rich pegmatites may be necessary. ^[3]

Chrysoberyl

Yellow chrysoberyl gemstone featuring oval step cut.

Chrysoberyl was discovered in 1789 and described and named by Abraham Gottlob Werner, in 1790. Abraham Gottlob Werner ( September 25, 1749 &ndash June 30, 1817) was a German Geologist who set out a now obsolete theory Werner worked at the Freiberg School of Mining from 1790-1793 and was well known as one of the most outstanding geologists of his time. He is best known today as the loser in the battle of the Neptunists and Vulcanists that raged in the 1780s. ^[4]

Chrysoberyl is normally yellow, yellow-green, or brownish with its color being caused by the presence of iron. Spectroscopic analysis will usually reveal a strong band where the violet takes over from the blue. As the color darkens from bright yellowish-green to golden-yellow to brown, this band increases in strength. When the stone has a strong color, two additional bands can be seen in the green-blue. The most common inclusions are liquid-filled cavities containing three-phase inclusions. Stepped twin planes may be apparent in some cases. Some very rare minty bluish-green chrysoberyls from Tanzania owe their color to the presence of Vanadium.

Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones. Members of the beryl group include emerald, aquamarine, and morganite while members of the chrysoberyl group include chrysoberyl, cymophane (cat's eye), and alexandrite. Beryl is a silicate and chrysoberyl is an oxide and although both beryl and chrysoberyl contain beryllium, they are separate gemstone species unrelated in any other way. The Mineral beryl is a Beryllium Aluminium cyclosilicate with the Chemical formula Be3Al2(SiO36 The Mineral beryl is a Beryllium Aluminium cyclosilicate with the Chemical formula Be3Al2(SiO36 Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 Because of the confusion between chrysoberyl and beryl, chrysoberyl is relatively unknown in its own right and the alexandrite variety is much more widely recognized. The only well-known natural gemstones harder than chrysoberyl are corundum and diamond.

Alexandrite

Natural Russian alexandrite 3. 01ct

The alexandrite variety displays a color change (alexandrite effect) dependent upon light, along with strong pleochroism. Pleochroism is an Optical phenomenon in which grains of a rock appear to be different colors when observed at different angles under a Petrographic microscope. Alexandrite results from small scale replacement of aluminium by chromium oxide, which is responsible for alexandrite's characteristic green to red color change. Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 Alexandrite from the Ural Mountains in Russia is green by daylight and red by incandescent light. Riphean redirects here For the time period see Riphean stage The Ural Mountains (Ура́льские го́ры Uralskiye Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending Other varieties of alexandrite may be yellowish or pink in daylight and a columbine or raspberry red by incandescent light. Wild Columbine ( Aquilegia canadensis) is a Wildflower of the Ranunculaceae family The raspberry (plural raspberries) is the edible Fruit of a multitude of plant species in the subgenus Idaeobatus of the genus Rubus The optimum or "ideal" color change would be fine emerald green to fine purplish red, but this is exceedingly rare. Because of their rarity and the color change capability, "ideal" alexandrite gems are some of the most expensive in the world.

According to a widely popular but controversial story, alexandrite was discovered by the Finnish mineralogist Nils Gustaf Nordenskiöld, (1792 -1866) on the tsarevitch Alexander's sixteenth birthday on April 17, 1834 and named alexandrite in honor of the future Tsar Alexander II of Russia. Nils Gustaf Nordenskiöld ( October 12, 1792 &ndash February 2, 1866) was a Finnish Mineralogist and a traveller Tsar csar and tzar redirect here For other uses see Tsar (disambiguation. Alexander (Aleksandr II Nikolaevich (Александр II Николаевич ( Moscow, 29 April 1818 – 13 March 1881 in St Sometimes, Nils Gustaf Nordenskiöld is confused with his son, Adolf Erik Nordenskjöld (1832–1901), also a famous Finnish geologist, mineralogist and arctic explorer who accompanied his father to the Ural Mountains to study the iron and copper mines at Tagilsk in 1853. Nils Gustaf Nordenskiöld ( October 12, 1792 &ndash February 2, 1866) was a Finnish Mineralogist and a traveller Baron (Nils Adolf Erik Nordenskiöld, also known as A E Nordenskioeld (November 18 1832 Helsinki, Finland &mdash August 12 1901 Dalby Skåne However, Adolf Erik Nordenskiöld was only two years old when Alexandrite was discovered and only ten years old when a description of the stone was published under the name of Alexandrite for the first time.

Alexandrite step cut cushion, 26. 75 cts. Alexandrites this large are extremely rare.

Although it was Nordenskiöld who discovered alexandrite, he could not possibly have discovered and named it on Alexander's birthday. Nordenskiöld's initial discovery occurred as a result of an examination of a newly found mineral sample he had received from Perovskii, which he identified as emerald at first. After the discovery of emeralds in the roots of an upturned tree, the first emerald mine had been opened in 1831, not long before Nordenskiöld had received this particular sample. ^[5]

Confused with the high hardness however, he decided to continue his examinations. Later that evening, while looking at the specimen under candlelight, he was surprised to see that the color of the stone had changed to raspberry-red instead of green. Later, he confirmed the discovery of a new variety of chrysoberyl, and suggested the name "diaphanite"^[2] (from the Greek "di-", twi- and "aphanès", inapparent).

The name of the first person to actually find this stone has been lost in the mists of time. However, the first person to bring it to public attention, and ensure that it would be forever associated with the Imperial family was Count Lev Alekseevich Perovskii (1792-1856. )^[6]

Natural Russian alexandrite gemstones

The finest alexandrites up to 5 carat is being found in the Ural Mountains, but the largest cut stones being in the 30 carat range, though many fine examples have been discovered in Sri Lanka (up to 65 cts. Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka ( Sinhalese:, இலங்கை known as Ceylon before 1972 is an Island ), India (Andhra Pradesh), Brazil, Myanmar, and especially Zimbabwe (small stones usually under 1 carat (200 mg) but with intense color change). India, officially the Republic of India (भारत गणराज्य inc-Latn Bhārat Gaṇarājya; see also other Indian languages) is a country |utc_offset = -2 to -4 |time_zone_DST = BRST |utc_offset_DST = -2 to -5 |cctld Burma, officially the Union of Myanmar ( pjìdàunzṵ mjàmmà nàinŋàndɔ̀ is the largest country by geographical area in mainland Southeast Asia. See also Great Zimbabwe National Monument. For information about the March and June 2008 presidential elections see Zimbabwean presidential election Overall, stones from any locale over 5 carats (1 g) would be considered extremely rare, especially gems with fine color change. Alexandrite is both hard and tough, making it very well suited to wear in jewelry.

The gem has given rise to the adjective "alexandritic", meaning any transparent gem or material which shows a noted change in color between natural and incandescent light. Some other gem varieties of which alexandritic specimens have been found include sapphire, garnet, and spinel. Sapphire (antique greek hyacinthos refers to gem varieties of the mineral Corundum, an Aluminium oxide (Al2O3 when it is a color other than The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives The spinels are any of a class of Minerals of general formulation XY2 O 4 which Crystallize in the cubic (isometric

Some gemstones described as lab-grown (synthetic) alexandrite are actually corundum laced with trace elements (e. g. , vanadium) or color-change spinel and are not actually chrysoberyl. Vanadium (vəˈneɪdiəm is a Chemical element that has the symbol V and Atomic number 23 The spinels are any of a class of Minerals of general formulation XY2 O 4 which Crystallize in the cubic (isometric As a result, they would be more accurately described as simulated alexandrite rather than synthetic but are often called Czochralski Alexandrite after the process that grows the crystals. The Czochralski process is a method of Crystal growth used to obtain Single crystals of Semiconductors (e

Synthetic alexandrite is used as an active laser medium. Synthetic alexandrite has been created by the Floating zone method. The active laser medium or gain medium is the source of optical Gain within a Laser. Alexandrite laser crystals tend to be round, with a pale brown tint.

Genuine alexandrite is one of the most expensive gemstones available commercially, with the stronger color changes being more highly valued. The following are average retail prices for alexandrite in December 2004 from The International Gem Society^[7]:

Cymophane

Fine color Cymophane with a sharp and centered eye.

Translucent yellowish chatoyant chyrsoberyl is called cymophane or cat's eye. In Gemology, chatoyancy (or chatoyance) is an optical reflectance effect seen in certain Gemstones Coined from the French "oeil de chat" Cymophane has its derivation also from the Greek words meaning 'wave' and 'appearance', in reference to the chatoyancy sometimes exhibited. In this variety, microscopic tubelike cavities or needlelike inclusions of rutile occur in an orientation parallel to the c-axis producing a chatoyant effect visible as a single ray of light passing across the crystal. Rutile is a Mineral composed primarily of Titanium dioxide, Ti[[oxygen O]]2 This effect is best seen in gemstones cut in cabochon form perpendicular to the c-axis. A cabochon or cabachon is a Gemstone which has been shaped and polished as opposed to Facetted The resulting form is usually a convex top with a The color in yellow chrysoberyl is due to Fe³⁺ impurities.

Although other minerals such as tourmaline, scapolite, corundum, spinel and quartz can form "cat's eye" stones similar in appearance to cymophane, the jewelry industry designates these stones as "quartz cat's eyes", or "ruby cat's eyes" and only chrysoberyl can be referred to as "cat's eye" with no other designation. Tourmaline is a Crystal Silicate mineral compounded with elements such as Aluminium, Iron, Magnesium, Sodium, Lithium Scapolite (Gr asairos, rod stone is a group of rock-forming Silicate minerals composed of Aluminium, Calcium and Sodium Silicate Corundum (from Tamil kurundam குருந்தம் or kuruvindam குருவிந்தம் is a Crystalline form of The spinels are any of a class of Minerals of general formulation XY2 O 4 which Crystallize in the cubic (isometric Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in

Gems lacking the silky inclusions required to produce the cat's eye effect is usually faceted. An alexandrite cat's eye is a chrysoberyl cat's eye that changes color. "Milk and honey" is a term commonly used to describe the color of the best cat's eyes. The effect refers to the sharp milky ray of white light normally crossing the cabochon as a center line along its length and overlying the honey colored background. The honey color is considered to be top by many gemologists but the lemon yellow colors are also popular and attractive. Cat's eye material is found as a small percentage of the overall chrysoberyl production wherever chrysoberyl is found.

Cat's eye really became popular by the end of the 19th century when the Duke of Connaught gave a ring with a cat's eye as an engagement token, this was sufficient to make the stone more popular and increase its value greatly. Up to that time cat's eye had predominantly been present in gem and mineral collections. The increased demand in its turn created an intensified search for it in Ceylon . Early 20th century prices could go up as high as $8000 for a cut stone. ^[8]

See also

• List of minerals
• List of minerals named after people
• Synthetic alexandrite

References

1. ^ Chrysoberyl In Webmineral. This is a List of Minerals for which there are Wikipedia articles This is a list of Minerals named after people. The chemical composition follows name when available Synthetic alexandrite has been created by the Floating zone method. Retrieved online 08:20, January 25, 2005
2. ^ ^{a b} Klein, Cornelis; and Cornelius S. Hurlbut, Jr. (1985). Manual of Mineralogy, 20th ed. , New York: Wiley. ISBN 0-471-80580-7.  
3. ^ Chapter 6: World Occurrences. (2006, February 07). In Alexandrite. net, Tsarstone collectors guide. Retrieved online 07:32, February 26, 2007
4. ^ Chapter 3: Species and variety. (2006, February 07). In Alexandrite. net, Tsarstone collectors guide. Retrieved online 06:45, February 26, 2007
5. ^ Sinkankas, J (1984). Gem Cutting, A Lapidary's Manual. van Nostrom Reinhold.  
6. ^ Chapter 2: Diaphanite or Alexandrite? (2006, December 07). In Alexandrite. net, Tsarstone collectors guide. Retrieved online 08:20, January 25, 2007
7. ^ Chapter 9: Alexandrite Buyer's Guide (2006, December 07). In Alexandrite. net, Tsarstone collectors guide. Retrieved online 16:16 PDT, August 9, 2007
8. ^ U.S. Geological Survey, 1887 , George Frederick Kunz, Cymophane, Cat's Eye as gemstone (1887). Retrieved on 2007-07-09. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 455 - Roman military commander Avitus is proclaimed Emperor of the Western Roman Empire.

External links

• Alexandrite guide
• Chrysoberyl classification from Webmineral
• Classification of chrysoberyl from Mindat