Dresden Castle or Royal Palace is one of the oldest buildings in Dresden, Germany. For 400 years, it was the residence of the electors and kings of Saxony of the Albertine line of the House of Wettin, it is known for the different architectural styles employed, from Baroque to Neo-renaissance. Today, the residential castle is a museum complex that contains the Historic and New Green Vault, the Numismatic Cabinet, the Collection of Prints and Photographs and the Dresden Armory with the Turkish Chamber, it houses an art library and the management of the Dresden State Art Collections. The original castle was a Romanesque keep, built around 1200; the Hausmannsturm was built at the beginning of the 15th century. From 1468 until 1480, the keep was extended by the master builder, Arnold von Westfalen, becoming an enclosed four-wing construction. In the middle of the 16th century, an addition was added in the Renaissance style. After a major fire in 1701, Augustus II the Strong rebuilt much of the castle in the Baroque style.
The collection rooms were created at this time in the western wing. The Silver Room, Heraldic Room and the Pretiosensaal were built from 1723–1726 and the Kaminzimmer, Ivory Room and Bronze Room were built from 1727–1729; the 800th anniversary of the House of Wettin, Saxony's ruling family, resulted in more rebuilding between 1889 and 1901. A Neo-renaissance renovation was undertaken, followed by various modernizations, such as in-floor heating and electric lights in 1914. On the outside of the Stallhof, which links the castle complex with the adjacent Johanneum, the "Procession of Princes" was painted by the artist Wilhelm Walther; the 102-meter-long mural represents the history of the Wettins. Since it faded, it was transferred to about 23,000 Meissen porcelain tiles between 1904 and 1907. Most of the castle was reduced to a roofless shell during the February 13, 1945 bombing of Dresden in World War II. Three rooms of the Green Vault were destroyed. However, the collections survived, having been moved to safety at Königstein Fortress in the early years of the war.
For the first 15 years after the end of the Second World War, no attempt was made to rebuild the castle, except to install a temporary roof in 1946. Restoration began in the 1960s with the installation of new windows and has occurred since then; the castle's restoration was completed in 2013. Dresden castle houses five museums, the Historic Green Vault and the New Green Vault, the Numismatic Cabinet, the Collection of Prints and Photographs and the Dresden Armory with the Turkish Chamber. Accessible is an art library with 260,000 volumes of special literature on art history; the character of the holdings is related to the collecting focal points of the museums. The Gallery of the Electors and the Hausmannsturm, once Dresden's largest tower, can be visited as well; the Green Vault is a museum. Founded by Augustus II the Strong in 1723, it features a unique and rich variety of exhibits from the period of baroque to classicism; the museum consists of the New Green Vault. The Historic Green Vault is known for its treasure chambers, is itself a baroque work of art.
The New Green Vault is more modern. The Historic Green Vault is located on the ground floor of the Dresden Castle and visits require an advance booking; the Numismatic Cabinet, with its nearly 300,000 pieces, is one of Dresden’s oldest museums, dating back to the early 16th century. It contains one of the largest universal collections in Europe, its broad spectrum ranges from classical antiquity to present-day coins. Some 30,000 Saxon coins and medals represent different periods in Saxony's history; the collection includes orders and insignia, bank notes and historic bonds, seals, minting dies for coins and medals, as well as minting machines and equipment. The exhibition is open from April to October, it shows around 300 outstanding objects, which represent a cross-section of the various parts of the collection. The Numismatic Cabinet is a center of scholarly research and has a public library of some 30,000 volumes; the Collection of Prints and Photographs shows work by renowned artists from numerous countries.
There are 515,000 objects by more than 20,000 artists across eight centuries. It holds drawings and prints by old masters such as Albrecht Dürer, Rembrandt and Caspar David Friedrich, as well as artists, like Henri de Toulouse-Lautrec and Pablo Picasso. Engravings by Martin Schongauer and woodcuts by Lucas Cranach the Elder are shown along with photographic works. There is a collection of drawings and graphic art by Käthe Kollwitz. Originating from weapons owned by Saxon Dukes and Electors, the Dresden Armory owns one of the most valuable collections of weapons and armory in the world; the exhibition includes around 10,000 objects, including helmets, swords, daggers and maces, pistols and rifles, riding equipment and ceremonial clothes. The Turkish Chamber is a separate collection within the Dresden Armory, focused on art from the Ottoman Empire, it displays more than 600 objects of art from the Ottoman Empire, making it one of the oldest and most significant collections outside Turkey. Between the 16th and the 19th centuries, the electors of Saxony, motivated by their passion for collecting and their desire for princely prestige
The Grünes Gewölbe in Dresden is a unique historic museum that contains the largest collection of treasures in Europe. Founded by Augustus the Strong in 1723, it features a rich variety of exhibits from the Baroque to Classicism, it is named after the malachite green painted column bases and capitals of the initial rooms. It has some claim to be the oldest museum in the world. After the devastation of World War II, the Grünes Gewölbe was restored. Today, its treasures are shown in two exhibitions: The Historic Green Vault is famous for its splendors of the historic treasure chamber as it existed in 1733, while the New Green Vault focuses the attention on each individual object in neutral rooms; the Grünes Gewölbe is located on the first and second floors of the western section of the Dresdner Residenzschloss. It is now part of the Dresden State Art Collections; the history of the "Green Vault" goes back to the year 1547, when elector Moritz of Saxony initiated the building of an additional west wing to the palace.
Four of the new rooms on the first floor were given molded plaster ceilings. The column bases and their capitals were painted with a characteristic bluish-green paint. Due to this color, the rooms were soon known as the "Green Vault", the name has endured; the official name of the suite of rooms, protected against fire and robbery by thick walls, iron shutters and doors, was "Privy Repository". Throughout the 17th century, these rooms were used by the rulers of Saxony as a private treasure chamber for important documents and jewellery. Between 1723 and 1729, the elector Frederic Augustus I, today known as Augustus the Strong, turned the once private chambers into a public museum. First, he commanded splendid rooms to be created in; the Pretiosensaal and the Eckkabinett were listed as completed in the inventory of 1725. An extension followed in 1727. Augustus' intentions have been preserved on a ground plan from 1727; as in the first construction phase, the architect Matthäus Daniel Pöppelmann planned and built a museum-like, artistic structure of German Baroque grandeur.
A suite of eight interconnecting rooms was constructed whose architectural beauty complemented the abundance and quality of the priceless treasures. Augustus the Strong could now exhibit his entire collection of valuables, including bronze statues and works of art in silver, gold and ivory; the sequence of rooms was deliberately staged. By the end of his four-decade-long reign in 1733, Augustus the Strong had made his crown treasures and his inherited riches accessible to the public – an unprecedented innovation in the Baroque period; these rooms remained unchanged for two centuries. When war was imminent in 1938, the art treasures were taken to the Königstein Fortress; the Green Vault was damaged in the February 13, 1945 bombing of Dresden in World War II. Three of the eight rooms were destroyed. At the end of the war in 1945, the treasures were confiscated by the Red Army and transported to the Soviet Union. After their return to Dresden in 1958, part of the collection was displayed at the Albertinum.
In 2004, the Neues Grünes Gewölbe was opened on the second floor of the rebuilt Dresden castle. Its modern style of presentation centers on the works of art. In 2006, the reconstructed Historisches Grünes Gewölbe was reopened in the magnificent suite of rooms on the first floor as it had existed in 1733 at the time of its founder's death; the whole collection consists of more than 4,000 pieces, with 1,100 in the New Green Vault and about 3,000 shown in the original Historic Green Vault. The Historic Green Vault is located on the first floor of the Dresden Castle and the New Green Vault on the second floor, each covering 2,000 square metres; the Historic Green Vault is famous for the splendors of the treasure chamber, in itself a baroque work of art, while the more modern New Green Vault focuses the attention on each individual object. Entrance to the Historic Green Vault requires advance purchase of tickets for a specific entry time slot. A limited number of tickets is sold every morning; the New Green Vault can be visited at any time.
The Historic Green Vault has on display 3,000 masterpieces of jewelry and the goldsmith's art, as well as precious objects made of amber and ivory. Gemstone vessels and elegant bronze statuettes are presented without showcases in front of ornate mirrored display walls. With these treasure chambers, Augustus the Strong realised his vision of a Baroque Gesamtkunstwerk as an expression of wealth and absolutist power, he presented his treasures to a select public, thus establishing the Green Vault as one of Europe's oldest museums. The Historic Green Vault consists of 9 rooms and one entrance chamber: The Vorgewölbe with Martin Luther-Kabinett: collection of Schatzkunst of the Middle Ages and early Renaissance and enamel works from Limoges; the Bernsteinkabinett: artworks made of amber. The Elfenbeinzimmer: great variety of carved art pieces and small statues, all made from real ivory; the Weißsilberzimmer: silver artworks, including silver table service of Augustus the Strong. The Si
Andhra Pradesh is one of the 29 states of India. Situated in the south-east of the country, it is the seventh-largest state in India, covering an area of 162,970 km2; as per the 2011 census, it is the tenth most populous state, with 49,386,799 inhabitants. The largest city in Andhra Pradesh is Visakhapatnam. Telugu, one of the classical languages of India, is the major and official language of Andhra Pradesh. On 2 June 2014, the north-western portion of Andhra Pradesh was separated to form the new state Telangana and the longtime capital of Andhra Pradesh, was transferred to Telangana as part of the division. However, in accordance with the Andhra Pradesh Reorganisation Act, 2014, Hyderabad was to remain as the acting capital of both Andhra Pradesh and Telangana states for a period of time not exceeding ten years; the new riverfront de facto capital, Amaravati, is under the jurisdiction of the Andhra Pradesh Capital Region Development Authority. Andhra Pradesh has a coastline of 974 km – the second longest coastline among the states of India, after Gujarat – with jurisdiction over 15,000 km2 of territorial waters.
The state is bordered by Telangana in the north-west and Odisha in the north-east, Karnataka in the west, Tamil Nadu in the south, to the east lies the Bay of Bengal. The small enclave of Yanam, a district of Puducherry, lies to the south of Kakinada in the Godavari delta on the eastern side of the state; the state is made up of the two major regions of Rayalaseema, in the inland southwestern part of the state, Coastal Andhra to the east and northeast, bordering the Bay of Bengal. The state comprises thirteen districts in total, nine of which are located in Coastal Andhra and four in Rayalaseema; the largest city and commercial hub of the state are Visakhapatnam, located on the Bay of Bengal, with a GDP of US$43.5 billion. The economy of Andhra Pradesh is the seventh-largest state economy in India with ₹8.70 lakh crore in gross domestic product and a per capita GDP of ₹142,000. Andhra Pradesh hosted 121.8 million visitors in 2015, a 30% growth in tourist arrivals over the previous year, making it the third most-visited state in India.
The Tirumala Venkateswara Temple in Tirupati is one of the world's most visited religious sites, with 18.25 million visitors per year. Other pilgrimage centres in the state include the Mallikarjuna Jyotirlinga at Srisailam, the Srikalahasteeswara Temple at Srikalahasti, the Ameen Peer Dargah in Kadapa, the Mahachaitya at Amaravathi, the Kanaka Durga Temple in Vijayawada, Prasanthi Nilayam in Puttaparthi; the state's natural attractions include the beaches of Visakhapatnam, hill stations such as the Araku Valley and Horsley Hills, the island of Konaseema in the Godavari River delta. A tribe named. According to Aitareya Brahmana of the Rig Veda, the Andhra left north India and settled in south India; the Satavahanas have been mentioned by the names Andhra, Andhrara-jateeya and Andhrabhrtya in the Puranic literature. They did not refer themselves as Andhra in any of their inscriptions. Archaeological evidence from places such as Amaravati and Vaddamanu suggests that the Andhra region was part of the Mauryan Empire.
Amaravati might have been a regional centre for the Mauryan rule. After the death of Emperor Ashoka, Mauryan rule weakened around 200 BCE and was replaced by several smaller kingdoms in the Andhra region; the Satavahana dynasty dominated the Deccan region from the 1st century BC to the 3rd century. The Satavahanas made Dharanikota and Amaravathi their capital, which according to the Buddhists is the place where Nagarjuna, the philosopher of Mahayana lived in the 2nd and 3rd centuries; the Andhra Ikshvakus, with their capital at Vijayapuri, succeeded the Satavahanas in the Krishna River valley in the latter half of the 2nd century. Pallavas, who were executive officers under the Satavahana kings, were not a recognised political power before the 2nd century AD and were swept away by the Western Chalukyan invasion, led by Pulakesin II in the first quarter of the 7th century CE. After the downfall of the Ikshvakus, the Vishnukundinas were the first great dynasty in the 5th and 6th centuries, held sway over the entire Andhra country, including Kalinga and parts of Telangana.
They played an important role in the history of Deccan during the 5th and 6th century CE, with Eluru and Puranisangam. The Salankayanas were an ancient dynasty that ruled the Andhra region between Godavari and Krishna with their capital at Vengi from 300 to 440 CE; the Eastern Chalukyas of Vengi, whose dynasty lasted for around five hundred years from the 7th century until 1130 C. E. merged with the Chola empire. They continued to rule under the protection of the Chola empire until 1189 C. E. when the kingdom succumbed to the Hoysalas and the Yadavas. The roots of the Telugu language have been seen on inscriptions found near the Guntur district and from others dating to the rule of Renati Cholas in the fifth century CE. Kakatiyas constructed several forts, they were succeeded by the Musunuri Nayaks. The Reddy dynasty was established by Prolaya Vema Reddi in the early 14th century, who ruled from present day Kondaveedu. Prolaya Vema Reddi was part of the confederation of states that started a movement against the invading Turkic Muslim armies of the Delhi
Diamond enhancements are specific treatments, performed on natural diamonds, which are designed to improve the visual gemological characteristics of the diamond in one or more ways. These include clarity treatments such as laser drilling to remove black carbon inclusions, fracture filling to make small internal cracks less visible, color irradiation and annealing treatments to make yellow and brown diamonds a vibrant fancy color such as vivid yellow, blue, or pink; the CIBJO and government agencies such as the United States Federal Trade Commission explicitly require the disclosure of all diamond treatments at the time of sale. Some treatments those applied to clarity, remain controversial within the industry—this arises from the traditional notion that diamonds hold a unique or "sacred" place among the gemstones, should not be treated too radically, if for no other reason than a fear of damaging consumer confidence. Clarity and color enhanced diamonds sell at lower price points when compared to similar, untreated diamonds.
This is because enhanced diamonds are lower quality before the enhancement is performed, therefore are priced at a substandard level. After enhancement, the diamonds may visually appear as good as their non-enhanced counterparts; the clarity, or purity, of a diamond refers to internal inclusions of the diamond, is one of the 4-C's in determining a diamonds' value. Common inclusions that appear inside diamonds are black carbon spots and small cracks referred to as fractures or "feathers", due to their feathery whitish appearance when viewed from above or through the side. Diamonds may have other inclusions such as air bubbles and mineral deposits such as iron or garnet; the size and position of the inclusions are factors in determining the value of a diamond when the other gemological characteristics are of a higher standard. The development of laser drilling techniques have increased the ability to selectively target and reduce the visibility of black carbon inclusions on a microscopic scale.
Diamonds containing hematite inclusions have been laser-drilled since the late 1960s, a technique credited to Louis Perlman that did a successful test a year after General Electric had made a similar one with a diamond for industrial use in 1962. The laser drilling process involves the use of an infrared laser to bore fine holes into a diamond to create a route of access to a black carbon crystal inclusion; because diamond is transparent to the wavelength of the laser beam, a coating of amorphous carbon or other energy-absorbent substance is applied to the surface of the diamond to initiate the drilling process. The laser burns a narrow tube or channel to the inclusion. Once the location of included black carbon crystal has been reached by the drill channel, the diamond is soaked in sulfuric acid to dissolve the black carbon crystal. After soaking in sulfuric acid the black carbon crystal will dissolve and become transparent and sometimes whitish opaque. Under microscopic inspection the fine drill or bore holes can be seen, but are not distracting and do not affect sparkle or brilliance of the diamond.
While the channels are straight in direction, from an entry point on the surface, some drilling techniques are drilled from within, using occurring fractures inside the stone to reach the inclusion in a way that mimics organic "feathers". The channels are microscopic so that debris can not travel down the channel; the surface-reaching holes can only be seen by reflecting light off of the surface of the diamond during microscopic viewing such as a jeweler's 10x magnifying lens or loupe and are invisible to the naked eye. While fracture filling as a method to enhance gems has been found in gems over 2,500 years old, the diamond's unique refractive index required a more advanced solution than simple wax and oil treatments; this technology became available 20 years after the time the laser drilling technique was developed. Put, "fracture filling" makes tiny natural fractures inside diamonds less visible to the naked eye or under magnification. Fractures are common inside diamonds and are created during the diamond's creation in the earth's crust.
As the rough diamond travels up from the earth's crust through volcanic pipes it comes under extreme stresses and pressures, during this travel tiny fractures can form inside the diamond. If these fractures are visible and damaging to the beauty of the diamond, it will have much lower demand and won't be as salable to jewelers and the general public, making them candidates for fracture filling and thus visually improve the appearance of the diamond; the fracture filling of diamond is the last step in the process of diamond enhancement, following laser drilling and acid-etching of inclusions, though if the fractures are surface-reaching, no drilling may be required. This process, which involves the use of specially-formulated solutions with a refractive index approximating that of diamond, was pioneered by Zvi Yehuda of Ramat Gan, Israel. Yehuda is now used as a brand name applied to diamonds treated in this manner. Koss & Schechter, another Israel-based firm, attempted to modify Yehuda's process in the 1990s by using halogen-based glasses, but this was unsuccessful.
The details behind the Yehuda process have been kept secret, but the filler used is reported to be lead oxychloride glass, which has a low melting point. The New York-based Dialase treats diamonds via a Yehuda-based process, which i
India known as the Republic of India, is a country in South Asia. It is the seventh largest country by area and with more than 1.3 billion people, it is the second most populous country as well as the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, the Bay of Bengal on the southeast, it shares land borders with Pakistan to the west. In the Indian Ocean, India is in the vicinity of Sri Lanka and the Maldives, while its Andaman and Nicobar Islands share a maritime border with Thailand and Indonesia; the Indian subcontinent was home to the urban Indus Valley Civilisation of the 3rd millennium BCE. In the following millennium, the oldest scriptures associated with Hinduism began to be composed. Social stratification, based on caste, emerged in the first millennium BCE, Buddhism and Jainism arose. Early political consolidations took place under the Gupta empires. In the medieval era, Zoroastrianism and Islam arrived, Sikhism emerged, all adding to the region's diverse culture.
Much of the north fell to the Delhi Sultanate. The economy expanded in the 17th century in the Mughal Empire. In the mid-18th century, the subcontinent came under British East India Company rule, in the mid-19th under British Crown rule. A nationalist movement emerged in the late 19th century, which under Mahatma Gandhi, was noted for nonviolent resistance and led to India's independence in 1947. In 2017, the Indian economy was the world's sixth largest by nominal GDP and third largest by purchasing power parity. Following market-based economic reforms in 1991, India became one of the fastest-growing major economies and is considered a newly industrialised country. However, it continues to face the challenges of poverty, corruption and inadequate public healthcare. A nuclear weapons state and regional power, it has the second largest standing army in the world and ranks fifth in military expenditure among nations. India is a federal republic governed under a parliamentary system and consists of 29 states and 7 union territories.
A pluralistic and multi-ethnic society, it is home to a diversity of wildlife in a variety of protected habitats. The name India is derived from Indus, which originates from the Old Persian word Hindush, equivalent to the Sanskrit word Sindhu, the historical local appellation for the Indus River; the ancient Greeks referred to the Indians as Indoi, which translates as "The people of the Indus". The geographical term Bharat, recognised by the Constitution of India as an official name for the country, is used by many Indian languages in its variations, it is a modernisation of the historical name Bharatavarsha, which traditionally referred to the Indian subcontinent and gained increasing currency from the mid-19th century as a native name for India. Hindustan is a Middle Persian name for India, it was introduced into India by the Mughals and used since then. Its meaning varied, referring to a region that encompassed northern India and Pakistan or India in its entirety; the name may refer to either the northern part of India or the entire country.
The earliest known human remains in South Asia date to about 30,000 years ago. Nearly contemporaneous human rock art sites have been found in many parts of the Indian subcontinent, including at the Bhimbetka rock shelters in Madhya Pradesh. After 6500 BCE, evidence for domestication of food crops and animals, construction of permanent structures, storage of agricultural surplus, appeared in Mehrgarh and other sites in what is now Balochistan; these developed into the Indus Valley Civilisation, the first urban culture in South Asia, which flourished during 2500–1900 BCE in what is now Pakistan and western India. Centred around cities such as Mohenjo-daro, Harappa and Kalibangan, relying on varied forms of subsistence, the civilization engaged robustly in crafts production and wide-ranging trade. During the period 2000–500 BCE, many regions of the subcontinent transitioned from the Chalcolithic cultures to the Iron Age ones; the Vedas, the oldest scriptures associated with Hinduism, were composed during this period, historians have analysed these to posit a Vedic culture in the Punjab region and the upper Gangetic Plain.
Most historians consider this period to have encompassed several waves of Indo-Aryan migration into the subcontinent from the north-west. The caste system, which created a hierarchy of priests and free peasants, but which excluded indigenous peoples by labeling their occupations impure, arose during this period. On the Deccan Plateau, archaeological evidence from this period suggests the existence of a chiefdom stage of political organisation. In South India, a progression to sedentary life is indicated by the large number of megalithic monuments dating from this period, as well as by nearby traces of agriculture, irrigation tanks, craft traditions. In the late Vedic period, around the 6th century BCE, the small states and chiefdoms of the Ganges Plain and the north-western regions had consolidated into 16 major oligarchies and monarchies that were known as the mahajanapadas; the emerging urbanisation gave rise to non-Vedic religious movements, two of which became independent religions. Jainism came into prominence during the life of Mahavira.
Buddhism, based on the teachings of Gautama Buddha, attracted followers from all social classes excepting the middle
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At room temperature and pressure, another solid form of carbon known as graphite is the chemically stable form, but diamond never converts to it. Diamond has the highest hardness and thermal conductivity of any natural material, properties that are utilized in major industrial applications such as cutting and polishing tools, they are the reason that diamond anvil cells can subject materials to pressures found deep in the Earth. Because the arrangement of atoms in diamond is rigid, few types of impurity can contaminate it. Small numbers of defects or impurities color diamond blue, brown, purple, orange or red. Diamond has high optical dispersion. Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometers in the Earth's mantle, although a few have come from as deep as 800 kilometers. Under high pressure and temperature, carbon-containing fluids dissolved minerals and replaced them with diamonds.
Much more they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites. Synthetic diamonds can be grown from high-purity carbon under high pressures and temperatures or from hydrocarbon gas by chemical vapor deposition. Imitation diamonds can be made out of materials such as cubic zirconia and silicon carbide. Natural and imitation diamonds are most distinguished using optical techniques or thermal conductivity measurements. Diamond is a solid form of pure carbon with its atoms arranged in a crystal. Solid carbon comes in different forms known as allotropes depending on the type of chemical bond; the two most common allotropes of pure carbon are graphite. In graphite the bonds are sp2 orbital hybrids and the atoms form in planes with each bound to three nearest neighbors 120 degrees apart. In diamond they are sp3 and the atoms form tetrahedra with each bound to four nearest neighbors. Tetrahedra are rigid, the bonds are strong, of all known substances diamond has the greatest number of atoms per unit volume, why it is both the hardest and the least compressible.
It has a high density, ranging from 3150 to 3530 kilograms per cubic metre in natural diamonds and 3520 kg/m³ in pure diamond. In graphite, the bonds between nearest neighbors are stronger but the bonds between planes are weak, so the planes can slip past each other. Thus, graphite is much softer than diamond. However, the stronger bonds make graphite less flammable. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity, as well as wide bandgap and high optical dispersion. Diamond's ignition point is 720 -- 800 °C in 850 -- 1000 °C in air; the equilibrium pressure and temperature conditions for a transition between graphite and diamond is well established theoretically and experimentally. The pressure changes linearly between 1.7 GPa at 0 K and 12 GPa at 5000 K. However, the phases have a wide region about this line where they can coexist. At normal temperature and pressure, 20 °C and 1 standard atmosphere, the stable phase of carbon is graphite, but diamond is metastable and its rate of conversion to graphite is negligible.
However, at temperatures above about 4500 K, diamond converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at 2000 K, a pressure of 35 GPa is needed. Above the triple point, the melting point of diamond increases with increasing pressure. At high pressures and germanium have a BC8 body-centered cubic crystal structure, a similar structure is predicted for carbon at high pressures. At 0 K, the transition is predicted to occur at 1100 GPa; the most common crystal structure of diamond is called diamond cubic. It is formed of unit cells stacked together. Although there are 18 atoms in the figure, each corner atom is shared by eight unit cells and each atom in the center of a face is shared by two, so there are a total of eight atoms per unit cell; each side of the unit cell is 3.57 angstroms in length. A diamond cubic lattice can be thought of as two interpenetrating face-centered cubic lattices with one displaced by 1/4 of the diagonal along a cubic cell, or as one lattice with two atoms associated with each lattice point.
Looked at from a <1 1 1> crystallographic direction, it is formed of layers stacked in a repeating ABCABC... pattern. Diamonds can form an ABAB... structure, known as hexagonal diamond or lonsdaleite, but this is far less common and is formed under different conditions from cubic carbon. Diamonds occur most as euhedral or rounded octahedra and twinned octahedra known as macles; as diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron. The crystals can be elongated. Diamonds are found coated in nyf, an opaque gum-like skin; some diamonds have opaque fibers. They are referred to as opaque if the fibers
A chemically pure and structurally perfect diamond is transparent with no hue, or color. However, in reality no gem-sized natural diamonds are perfect; the color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. For example, most white diamonds are discounted in price when more yellow hue is detectable, while intense pink diamonds or blue diamonds can be more valuable. Of all colored diamonds, red diamonds are the rarest; the Aurora Pyramid of Hope displays a spectacular array of colored diamonds, including red diamonds. Diamonds occur in a variety of colors—steel gray, blue, orange, green, pink to purple and black. Colored diamonds contain interstitial impurities or structural defects that cause the coloration, pure diamonds are transparent and colorless. Diamonds are scientifically classed into two main types and several subtypes, according to the nature of impurities present and how these impurities affect light absorption: Type I diamonds have nitrogen atoms as the main impurity at a concentration of 0.1%.
If the nitrogen atoms are in pairs they do not affect the diamond's color. If the nitrogen atoms are in large even-numbered aggregates they impart a yellow to brown tint. About 98% of gem diamonds are type Ia, most of these are a mixture of IaA and IaB material: these diamonds belong to the Cape series, named after the diamond-rich region known as Cape Province in North Africa, whose deposits are Type Ia. If the nitrogen atoms are dispersed throughout the crystal in isolated sites, they give the stone an intense yellow or brown tint. Synthetic diamond containing nitrogen is Type Ib. Type I diamonds absorb from 320 nm, they have a characteristic fluorescence and visible absorption spectrum. Type II diamonds have no measurable nitrogen impurities. Type II diamonds absorb in a different region of the infrared, transmit in the ultraviolet below 225 nm, unlike Type I diamonds, they have differing fluorescence characteristics, but no discernible visible absorption spectrum. Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising through plastic deformation during crystal growth—these diamonds are rare, but constitute a large percentage of Australian production.
Type IIb diamonds, which account for 0.1% of gem diamonds, are light blue due to scattered boron within the crystal matrix. However, a blue-grey color may occur in Type Ia diamonds and be unrelated to boron. Not restricted to type are green diamonds, whose color is caused by GR1 color centers in the crystal lattice produced by exposure to varying quantities of radiation. Pink and red are caused by plastic deformation of the crystal lattice from pressure. Black diamonds are caused by microscopic black or gray inclusions of other materials such as graphite or sulfides and/or microscopic fractures. Opaque or opalescent white diamonds are caused by microscopic inclusions. Purple diamonds are caused by a combination of high hydrogen content; the majority of diamonds that are mined are in a range of pale yellow or brown color, termed the normal color range. Diamonds that are of intense yellow or brown, or any other color are called fancy color diamonds. Diamonds that are of the highest purity are colorless, appear a bright white.
The degree to which diamonds exhibit body color is one of the four value factors by which diamonds are assessed. Diamonds have a color grading system; this system goes from D to Z. The more colorless a diamond is, the rarer and more valuable it is because it appears white and brighter to the eye. Color grading of diamonds was performed as a step of sorting rough diamonds for sale by the London Diamond Syndicate; as the diamond trade developed, early diamond grades were introduced by various parties in the diamond trade. Without any co-operative development these early grading systems lacked standard nomenclature, consistency; some early grading scales were. Numerous terms developed to describe diamonds of particular colors: golconda, jagers, blue white, fine white, gem blue, etc. Refers to a grading scale for diamonds in the normal color range used by internationally recognized laboratories; the scale ranges from D, colorless to Z, a pale yellow or brown color. Brown diamonds darker than K color are described using their letter grade, a descriptive phrase, for example M Faint Brown.
Diamonds with more depth of color than Z color fall into the fancy color diamond range. Diamond color is graded by comparing a sample stone to a master stone set of diamonds; each master stone is known to exhibit the least amount of body color that a diamond in that color grade may exhibit. A trained diamond grader compares a diamond of unknown grade against the series of master stones, assessing where in the range of color the diamond resides; this process occurs in a lighting box, fitted with daylight equivalent lamps. Accurate color grading can only be performed with diamond unset, as the comparison with master