Crystallographic defects in diamond
Imperfections in the crystal lattice of diamond are common. Such crystallographic defects in diamond may be the result of irregularities or extrinsic substitutional or interstitial impurities. Absorption spectrum is used not only to identify the defects, but to estimate their concentration, there is a tradition in diamond spectroscopy to label a defect-induced spectrum by a numbered acronym. This tradition has been followed in general with some notable deviations, many acronyms are confusing though, Some symbols are too similar. Accidentally, same labels were given to different centers detected by EPR, whereas some acronyms are logical, such as N3 or H3, many are not. In particular, there is no distinction between the meaning of labels GR, R and TR. The symmetry of defects in crystals is described by the point groups and they differ from the space groups describing the symmetry of crystals by absence of translations, and thus are much fewer in number. In diamond, only defects of the following symmetries have been observed thus far, tetragonal, the defect symmetry allows predicting many optical properties.
For example, one-phonon absorption in pure diamond lattice is forbidden because the lattice has an inversion center, introducing any defect breaks the crystal symmetry resulting in defect-induced infrared absorption, which is the most common tool to measure the defect concentrations in diamond. In synthetic diamond grown by the high-pressure high-temperature synthesis or chemical vapor deposition, such alignment has been been observed in gallium arsenide and thus is not unique to diamond. Various elemental analyses of diamond reveal a range of impurities. They mostly originate, from inclusions of foreign materials in diamond, virtually any element can be hammered into diamond by ion implantation. More essential are elements which can be introduced into the lattice as isolated atoms during the diamond growth. By 2008, those elements are nitrogen, hydrogen, phosphorus, cobalt and tungsten have been unambiguously detected in diamond, but they might originate from foreign inclusions. Detection of isolated iron in diamond has been re-interpreted in terms of micro-particles of ruby produced during the diamond synthesis, oxygen is believed to be a major impurity in diamond, but it has not been spectroscopically identified in diamond yet.
Two electron paramagnetic resonance centers have been assigned to nitrogen–oxygen complexes, the assignment is indirect and the corresponding concentrations are rather low. The most common impurity in diamond is nitrogen, which can comprise up to 1% of a diamond by mass. Previously, all defects in diamond were thought to be the result of structural anomalies, research revealed nitrogen to be present in most diamonds
The pound or pound-mass is a unit of mass used in the imperial, United States customary and other systems of measurement. The international standard symbol for the pound is lb. The unit is descended from the Roman libra, the English word pound is cognate with, among others, German Pfund, Dutch pond, and Swedish pund. All ultimately derive from a borrowing into Proto-Germanic of the Latin expression lībra pondō, usage of the unqualified term pound reflects the historical conflation of mass and weight. This accounts for the modern distinguishing terms pound-mass and pound-force, the United States and countries of the Commonwealth of Nations agreed upon common definitions for the pound and the yard. Since 1 July 1959, the avoirdupois pound has been defined as exactly 0.45359237 kg. In the United Kingdom, the use of the pound was implemented in the Weights and Measures Act 1963.9144 metre exactly. An avoirdupois pound is equal to 16 avoirdupois ounces and to exactly 7,000 grains, the conversion factor between the kilogram and the international pound was therefore chosen to be divisible by 7, and an grain is thus equal to exactly 64.79891 milligrams.
The US has not adopted the system despite many efforts to do so. Historically, in different parts of the world, at different points in time, and for different applications, the libra is an ancient Roman unit of mass that was equivalent to approximately 328.9 grams. It was divided into 12 unciae, or ounces, the libra is the origin of the abbreviation for pound, lb. A number of different definitions of the pound have historically used in Britain. Amongst these were the avoirdupois pound and the tower, merchants. Historically, the sterling was a tower pound of silver. In 1528, the standard was changed to the Troy pound, the avoirdupois pound, known as the wool pound, first came into general use c. It was initially equal to 6992 troy grains, the pound avoirdupois was divided into 16 ounces. During the reign of Queen Elizabeth, the pound was redefined as 7,000 troy grains. Since then, the grain has often been a part of the avoirdupois system
Ceratonia siliqua, commonly known as the carob tree, St Johns-bread, or locust bean, or simply locust-tree, is a species of flowering evergreen shrub or tree in the pea family, Fabaceae. It is widely cultivated for its edible pods, and as a tree in gardens. The ripe, dried pod is often ground to carob powder, Carob bars, an alternative to chocolate bars, are often available in health-food stores. The carat, a unit of mass for gemstones, and of purity for gold, takes its name, from the Greek word for a carob seed, the Ceratonia siliqua tree grows up to 15 m tall. The crown is broad and semispherical, supported by a trunk with brown rough bark. Leaves are 10 to 20 cm long, pinnate and it is frost-tolerant to roughly 20 °F. Most carob trees are dioecious, some are hermaphrodite, the male trees do not produce fruit. The fruit is a legume, that can be elongated, straight, or curved, the pods take a full year to develop and ripen. The sweet ripe pods eventually fall to the ground and are eaten by mammals, such as swine.
The seeds contain leucodelphinidin, a chemical compound. Although used extensively for agriculture, carob can still be growing wild in eastern Mediterranean regions. The common Greek name is, or, meaning wooden horn, in Turkey, it is known as keçiboynuzu, meaning goats horn. The various trees known as algarrobo in Latin America belong to a different subfamily, the carob genus, belongs to the Fabaceae family, and is believed to be an archaic remnant of a part of this family now generally considered extinct. It grows well in temperate and subtropical areas, and tolerates hot. As a xerophyte species, carob is well adapted to the conditions of the Mediterranean region with 250 to 500 mm of rainfall per year. Carob trees can survive long periods, but to grow fruit. Trees prefer well-drained, sandy loams and are intolerant of waterlogging, after irrigation with saline water in summer, carob trees could possibly recover during rainfalls in winter. In some experiments young carob trees could uphold basical physiological functions at 40 mmol NaCl/l, not all legume species can develop a symbiosis with rhizobia to use atmospheric nitrogen
Livorno is a port city on the Ligurian Sea on the western coast of Tuscany, Italy. It is the capital of the Province of Livorno, having a population of 159,431 residents in February 2015 and it has traditionally been known in English as Leghorn, pronounced /lɛˈɡɔːrn/ leg-AWRN, or /ˈlɛɡhɔːrn/ LEG-hawrn. The construction of the Via Aurelia coincided with the occupation of the region by the Romans, the natural cove called Liburna, transformed in Livorna in Livorno, is a reference to the type of ship, the liburna, used by Roman navy. Others ancient toponyms include, Antignano which was the place situated before Ardenza where were the beacons for the ships directed to Porto Pisano. The name Livorna is mentioned for the first time in 1017 as a coastal village, the port. In 1077 a tower was built by Matilda of Tuscany, the Republic of Pisa possessed Livorno from 1103 and built there a quadrangular Fort called Quadratura dei Pisani in defence of the port. Porto Pisano was destroyed after the defeat of the Pisan fleet in the Battle of Meloria in 1284.
Livorno was bought in 1399 by the Visconti of Milan, was sold to the Republic of Genoa in 1405, between 1427 and 1429, the census was held. According to the results of the census, there were 118 families in Livorno, Jews, military personnel, and the homeless were not included in the census. In 1551 the population was 1562 residents, in 1745 it had risen to 32,534, the only remainder of medieval Livorno is a fragment of two towers and a wall, located inside the Fortezza Vecchia. Livorno was designed as an Ideal town during the Italian Renaissance, the Porto Mediceo was overlooked and defended by towers and fortresses leading to the town centre. In the late 1580s, Ferdinando I de Medici, Grand Duke of Tuscany, declared Livorno a free port, to regulate this trade, in 1593 the Dukes administration established the Leggi Livornine. These laws were in force until 1603, until the beginning of the Counter-Reformation, the laws established a well-regulated market, protecting merchant activities from crime and racketeering, and instituted laws regarding international trade.
Additionally, expanding Christian tolerance, the offered the right of public freedom of religion. Livorno became an enlightened European city and one of the most important ports of the entire Mediterranean Basin, many European foreigners moved to Livorno. These included Christian Protestant reformers who supported such leaders as Martin Luther, John Calvin, French and English arrived, along with Orthodox Greeks. Meanwhile, Jews continued to trade under their previous treaties with the Grand Duke, on 19 March 1606, Ferdinando I de Medici elevated Livorno to the rank of city, the ceremony was held in the Fortezza Vecchia Chapel of Francis of Assisi. The Counter-Reformation increased tensions among Christians, dissidents to the Papacy were targeted by various Catholic absolute rulers, livornos tolerance fell victim to the European wars of religion
Bucharest is the capital and largest city of Romania, as well as its cultural and financial centre. It is located in the southeast of the country, at 44°25′57″N 26°06′14″E, on the banks of the Dâmbovița River, less than 60 km north of the Danube River, Bucharest was first mentioned in documents in 1459. It became the capital of Romania in 1862 and is the centre of Romanian media and its architecture is a mix of historical, communist-era and modern. In the period between the two World Wars, the citys elegant architecture and the sophistication of its elite earned Bucharest the nickname of Little Paris. Although buildings and districts in the city centre were heavily damaged or destroyed by war, earthquakes. In recent years, the city has been experiencing an economic, in 2016, the historical city centre was listed as endangered by the World Monuments Watch. According to the 2011 census,1,883,425 inhabitants live within the city limits, the urban area extends beyond the limits of Bucharest proper and has a population of about 1.9 million people.
Adding the satellite towns around the area, the proposed metropolitan area of Bucharest would have a population of 2.27 million people. According to Eurostat, Bucharest has an urban zone of 2,183,091 residents. According to unofficial data, the population is more than 3 million, Bucharest is the sixth-largest city in the European Union by population within city limits, after London, Madrid and Paris. Economically, Bucharest is the most prosperous city in Romania and is one of the industrial centres. The city has big convention facilities, educational institutes, cultural venues, traditional shopping arcades, the Romanian name București has an uncertain origin. Tradition connects the founding of Bucharest with the name of Bucur, who was a prince, an outlaw, a fisherman, in Romanian, the word stem bucurie means joy, and it is believed to be of Dacian origin. Other etymologies are given by scholars, including the one of an Ottoman traveler, Evliya Çelebi. A native or resident of Bucharest is called a Bucharester, Bucharests history alternated periods of development and decline from the early settlements in antiquity until its consolidation as the national capital of Romania late in the 19th century.
First mentioned as the Citadel of București in 1459, it became the residence of the famous Wallachian prince Vlad III the Impaler, the Ottomans appointed Greek administrators to run the town from the 18th century. A short-lived revolt initiated by Tudor Vladimirescu in 1821 led to the end of the rule of Constantinople Greeks in Bucharest, the Old Princely Court was erected by Mircea Ciobanul in the mid-16th century. Under subsequent rulers, Bucharest was established as the residence of the royal court
Cyprus, officially the Republic of Cyprus, is an island country in the Eastern Mediterranean and the third largest and third most populous island in the Mediterranean. It is located south of Turkey, west of Syria and Lebanon, northwest of Israel and Palestine, north of Egypt, the earliest known human activity on the island dates to around the 10th millennium BC. Archaeological remains from this include the well-preserved Neolithic village of Khirokitia. Cyprus was settled by Mycenaean Greeks in two waves in the 2nd millennium BC, Cyprus was placed under British administration based on Cyprus Convention in 1878 and formally annexed by Britain in 1914. While Turkish Cypriots made up 18% of the population, the partition of Cyprus and creation of a Turkish state in the north became a policy of Turkish Cypriot leaders, following nationalist violence in the 1950s, Cyprus was granted independence in 1960. On 15 July 1974, a coup détat was staged by Greek Cypriot nationalists and elements of the Greek military junta in an attempt at enosis and these events and the resulting political situation are matters of a continuing dispute.
The Cyprus Republic has de jure sovereignty over the island of Cyprus, as well as its territorial sea and exclusive economic area, another nearly 4% of the islands area is covered by the UN buffer zone. The international community considers the part of the island as territory of the Republic of Cyprus occupied by Turkish forces. The occupation is viewed as illegal under law, amounting to illegal occupation of EU territory since Cyprus became a member of the European Union. Cyprus is a major tourist destination in the Mediterranean, on 1 January 2008, the Republic of Cyprus joined the eurozone. The earliest attested reference to Cyprus is the 15th century BC Mycenaean Greek
Florence is the capital city of the Italian region of Tuscany and of the Metropolitan City of Florence. It is the most populous city in Tuscany, with 383,083 inhabitants, Florence was a centre of medieval European trade and finance and one of the wealthiest cities of the time. It is considered the birthplace of the Renaissance, and has called the Athens of the Middle Ages. A turbulent political history includes periods of rule by the powerful Medici family, from 1865 to 1871 the city was the capital of the recently established Kingdom of Italy. The Historic Centre of Florence attracts 13 million tourists each year and it was declared a World Heritage Site by UNESCO in 1982. The city is noted for its culture, Renaissance art and architecture, the city contains numerous museums and art galleries, such as the Uffizi Gallery and the Palazzo Pitti, and still exerts an influence in the fields of art and politics. Due to Florences artistic and architectural heritage, it has been ranked by Forbes as one of the most beautiful cities in the world, in 2008, the city had the 17th highest average income in Italy.
Florence originated as a Roman city, and later, after a period as a flourishing trading and banking medieval commune. According to the Encyclopædia Britannica, it was politically and culturally one of the most important cities in Europe, the language spoken in the city during the 14th century was, and still is, accepted as the Italian language. Starting from the late Middle Ages, Florentine money—in the form of the gold florin—financed the development of all over Europe, from Britain to Bruges, to Lyon. Florentine bankers financed the English kings during the Hundred Years War and they similarly financed the papacy, including the construction of their provisional capital of Avignon and, after their return to Rome, the reconstruction and Renaissance embellishment of Rome. Florence was home to the Medici, one of European historys most important noble families, Lorenzo de Medici was considered a political and cultural mastermind of Italy in the late 15th century. Two members of the family were popes in the early 16th century, Leo X, catherine de Medici married king Henry II of France and, after his death in 1559, reigned as regent in France.
Marie de Medici married Henry IV of France and gave birth to the future king Louis XIII, the Medici reigned as Grand Dukes of Tuscany, starting with Cosimo I de Medici in 1569 and ending with the death of Gian Gastone de Medici in 1737. The Etruscans initially formed in 200 BC the small settlement of Fiesole and it was built in the style of an army camp with the main streets, the cardo and the decumanus, intersecting at the present Piazza della Repubblica. Situated along the Via Cassia, the route between Rome and the north, and within the fertile valley of the Arno, the settlement quickly became an important commercial centre. Peace returned under Lombard rule in the 6th century, Florence was conquered by Charlemagne in 774 and became part of the Duchy of Tuscany, with Lucca as capital. The population began to again and commerce prospered
A diamond is one of the best-known and most sought-after gemstones. Diamonds have been known to mankind and used as decorative items since ancient times, the hardness of diamond and its high dispersion of light—giving the diamond its characteristic fire—make it useful for industrial applications and desirable as jewelry. Diamonds are such a highly traded commodity that multiple organizations have created for grading and certifying them based on the four Cs, which are color, clarity. Other characteristics, such as presence or lack of fluorescence, affect the desirability, the most famous use of the diamond in jewelry is in engagement rings. The practice is documented among European aristocracy as early as the 15th century, though ruby, the modern popularity of diamonds was largely created by De Beers Consolidated Mines Ltd. which established the first large-scale diamonds mines in South Africa. Through an advertising campaign beginning in the 1930s and continuing into the century, De Beers made diamonds into a key part of the betrothal process.
The diamonds high value has been the force behind dictators and revolutionary entities, especially in Africa, using slave. The value of diamonds is attributed largely to the tight control over this supply. Early references to diamonds in India come from Sanskrit texts, the Arthashastra of Kautilya mentions diamond trade in India. Buddhist works dating from the 4th century BC describe the diamond as a well-known and precious stone, golconda served as an important center for diamonds in central India. Diamonds were traded to both the east and west of India and were recognized by various cultures for their gemological or industrial uses. In his work Naturalis Historia, the Roman writer Pliny the Elder noted diamonds ornamental uses, diamonds eventually spread throughout the world, even though India had remained the only major source of the gemstone until the discovery of diamonds in Brazil in 1725. A Chinese work from the 3rd century BC mentions, Foreigners wear it in the belief that it can ward off evil influences.
The Chinese, who did not find diamonds in their country, initially did not use diamond as a jewel, diamonds reached ancient Rome from India. Diamonds were discovered in 700 AD in Borneo, and were used by the traders of southeast Asia, the modern era of diamond mining began in the 1860s in Kimberley, South Africa with the opening of the first large-scale diamond mine. The first diamond there was found in 1866 on the banks of the Orange River, in 1869, an even larger 83.50 carat diamond was found on the slopes of Colesberg Kopje on the farm Vooruitzigt belonging to the De Beers brothers. This sparked off the famous New Rush and within a month,800 claims were cut into the hillock which were worked frenetically by two to three thousand men, as the land was lowered so the hillock became a mine—in time, the world-renowned Kimberley Mine. Following agreement by the British government on compensation to the Orange Free State for its land claims
Lisbon is the capital and the largest city of Portugal, with a population of 552,700 within its administrative limits in an area of 100.05 km². Its urban area extends beyond the administrative limits with a population of around 2.7 million people. About 2.8 million people live in the Lisbon Metropolitan Area and it is continental Europes westernmost capital city and the only one along the Atlantic coast. Lisbon lies in the western Iberian Peninsula on the Atlantic Ocean, the westernmost areas of its metro area is the westernmost point of Continental Europe. Lisbon is recognised as a city because of its importance in finance, media, arts, international trade, education. It is one of the economic centres on the continent, with a growing financial sector. Humberto Delgado Airport serves over 20 million passengers annually, as of 2015, and the motorway network, the city is the 7th-most-visited city in Southern Europe, after Istanbul, Barcelona, Madrid and Milan, with 1,740,000 tourists in 2009. The Lisbon region contributes with a higher GDP PPP per capita than any region in Portugal.
Its GDP amounts to 96.3 billion USD and thus $32,434 per capita, the city occupies 32nd place of highest gross earnings in the world. Most of the headquarters of multinationals in the country are located in the Lisbon area and it is the political centre of the country, as its seat of Government and residence of the Head of State. Lisbon is one of the oldest cities in the world, julius Caesar made it a municipium called Felicitas Julia, adding to the name Olissipo. Ruled by a series of Germanic tribes from the 5th century, in 1147, the Crusaders under Afonso Henriques reconquered the city and since it has been a major political and cultural centre of Portugal. Unlike most capital cities, Lisbons status as the capital of Portugal has never been granted or confirmed officially – by statute or in written form. Its position as the capital has formed through constitutional convention, making its position as de facto capital a part of the Constitution of Portugal. It has one of the warmest winters of any metropolis in Europe, the typical summer season lasts about four months, from June to September, although in April temperatures sometimes reach around 25 °C.
Although modern archaeological excavations show a Phoenician presence at this location since 1200 BC, another conjecture based on ancient hydronymy suggests that the name of the settlement derived from the pre-Roman appellation for the Tagus, Lisso or Lucio. Lisbons name was written Ulyssippo in Latin by the geographer Pomponius Mela and it was referred to as Olisippo by Pliny the Elder and by the Greeks as Olissipo or Olissipona. The Indo-European Celts invaded in the 1st millennium BC, mixing with the Pre-Indo-European population and this indigenous settlement maintained commercial relations with the Phoenicians, which would account for the recent findings of Phoenician pottery and other material objects
Chennai /ˈtʃɛnnaɪ/, formerly known as Madras /məˈdrɑːs/ or /-ˈdræs/) is the capital of the Indian state of Tamil Nadu. Located on the Coromandel Coast off the Bay of Bengal, it is one of the biggest cultural, according to the 2011 Indian census, it is the sixth-largest city and fourth-most populous urban agglomeration in India. The city together with the adjoining regions constitute the Chennai Metropolitan Area, Chennai is among the most visited Indian cities by foreign tourists. It was ranked 43rd most visited city in the world for year 2015, the Quality of Living Survey rated Chennai as the safest city in India. Chennai attracts 45 percent of tourists visiting India, and 30 to 40 percent of domestic health tourists. As such, it is termed Indias health capital, as a growing metropolitan city in a developing country, Chennai confronts substantial pollution and other logistical and socio-economic problems. Chennai has the third-largest expatriate population in India at 35,000 in 2009,82,790 in 2011, tourism guide publisher Lonely Planet named Chennai as one of the top ten cities in the world to visit in 2015.
Chennai is ranked as a city in the Global Cities Index and was ranked the best city in India by India Today in the 2014 annual Indian city survey. In 2015 Chennai was named the hottest city by the BBC, National Geographic ranked Chennais food as second best in the world, it was the only Indian city to feature in the list. Chennai was named the ninth-best cosmopolitan city in the world by Lonely Planet, the Chennai Metropolitan Area is one of the largest city economies of India. Chennai is nicknamed The Detroit of India, with more than one-third of Indias automobile industry being based in the city, in January 2015, it was ranked third in terms of per capita GDP. Chennai has been selected as one of the 100 Indian cities to be developed as a city under PM Narendra Modis flagship Smart Cities Mission. The name Madras originated even before the British presence was established in India, the name Madras is said to have originated from a Portuguese phrase mae de Deus which means mother of god, due to Portuguese influence on the port city.
According to some sources, Madras was derived from Madraspattinam, a north of Fort St George. However, it is whether the name was in use before the arrival of Europeans. The British military mapmakers believed Madras was originally Mundir-raj or Mundiraj, Madras might have been derived from the word Madhuras meaning juice of honey or sugarcane in Sanskrit. The nativity of name Chennai, being of Telugu origin is clearly proved by the historians. The first official use of the name Chennai is said to be in a deed, dated 8 August 1639
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom or Britain, is a sovereign country in western Europe. Lying off the north-western coast of the European mainland, the United Kingdom includes the island of Great Britain, Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state—the Republic of Ireland. The Irish Sea lies between Great Britain and Ireland, with an area of 242,500 square kilometres, the United Kingdom is the 78th-largest sovereign state in the world and the 11th-largest in Europe. It is the 21st-most populous country, with an estimated 65.1 million inhabitants, this makes it the fourth-most densely populated country in the European Union. The United Kingdom is a monarchy with a parliamentary system of governance. The monarch is Queen Elizabeth II, who has reigned since 6 February 1952, other major urban areas in the United Kingdom include the regions of Birmingham, Glasgow and Manchester.
The United Kingdom consists of four countries—England, Wales, the last three have devolved administrations, each with varying powers, based in their capitals, Edinburgh and Belfast, respectively. The relationships among the countries of the UK have changed over time, Wales was annexed by the Kingdom of England under the Laws in Wales Acts 1535 and 1542. A treaty between England and Scotland resulted in 1707 in a unified Kingdom of Great Britain, which merged in 1801 with the Kingdom of Ireland to form the United Kingdom of Great Britain and Ireland. Five-sixths of Ireland seceded from the UK in 1922, leaving the present formulation of the United Kingdom of Great Britain, there are fourteen British Overseas Territories. These are the remnants of the British Empire which, at its height in the 1920s, British influence can be observed in the language and legal systems of many of its former colonies. The United Kingdom is a country and has the worlds fifth-largest economy by nominal GDP. The UK is considered to have an economy and is categorised as very high in the Human Development Index.
It was the worlds first industrialised country and the worlds foremost power during the 19th, the UK remains a great power with considerable economic, military and political influence internationally. It is a nuclear weapons state and its military expenditure ranks fourth or fifth in the world. The UK has been a permanent member of the United Nations Security Council since its first session in 1946 and it has been a leading member state of the EU and its predecessor, the European Economic Community, since 1973. However, on 23 June 2016, a referendum on the UKs membership of the EU resulted in a decision to leave. The Acts of Union 1800 united the Kingdom of Great Britain, Scotland and Northern Ireland have devolved self-government
A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks or organic materials that are not minerals are used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone, apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gemcutter, a worker is a diamantaire. The carvings of Carl Fabergé are significant works in this tradition, the traditional classification in the West, which goes back to the ancient Greeks, begins with a distinction between precious and semi-precious, similar distinctions are made in other cultures. In modern usage the precious stones are diamond, sapphire, other stones are classified by their color and hardness.
Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone, in modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition, for example, diamonds are made of carbon and rubies of aluminium oxide. Next, many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic, another term used is habit, the form the gem is usually found in. For example, which have a crystal system, are often found as octahedrons. Gemstones are classified into different groups and varieties, for example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the Emerald, red beryl, goshenite and morganite, gems are characterized in terms of refractive index, specific gravity, cleavage and luster.
They may exhibit pleochroism or double refraction and they may have luminescence and a distinctive absorption spectrum. Material or flaws within a stone may be present as inclusions, gemstones may be classified in terms of their water. This is a grading of the gems luster, transparency. Very transparent gems are considered first water, while second or third water gems are those of a lesser transparency, there is no universally accepted grading system for gemstones. Diamonds are graded using a system developed by the Gemological Institute of America in the early 1950s, all gemstones were graded using the naked eye