Diamond
In mineral science, diamond (gemstone) is an allotrope of carbon, in which the carbon atoms are arranged in a variation of the face-centered cubic crystal structure known as a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions. Diamond well known like a material with superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. Particularly, diamond has the highest hardness and thermal conductivity associated with a bulk material. Those properties determine the major industrial application of diamond in cutting and polishing tools.
Diamond holds remarkable optical characteristics. Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron and nitrogen. Coupled with wide transparency, this results in the clear, colorless appearance on most natural diamonds. Small amounts of defects or impurities (about one per million of lattice atoms) color diamond blue (boron), yellow (nitrogen), brown (lattice defects), green, purple, pink, orange or red. Diamond also has relatively high optical dispersion (ability to disperse light of different colors), which results in the characteristic luster. Excellent optical and mechanical properties, combined with efficient marketing, make diamond typically the most popular gemstone.
Most of the natural diamonds are formed at high-pressure high-temperature conditions existing at depths of 140 to 190 kilometers (87 to 120 mi) within the Earth mantle. Carbon-containing minerals supply the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years (25% to 75% of the chronilogical age of the Earth). Diamonds are brought close to the Earth surface through deep volcanic eruptions by a magma, which cools into igneous rocks referred to as kimberlites and lamproites. Diamonds can also be produced synthetically inside a high-pressure high-temperature process which approximately simulates the conditions in the Earth mantle. An alternate, and different growth way is chemical vapor deposition (CVD). Several non-diamond materials, which include cubic zirconia and silicon carbide and therefore are often called diamond simulants, resemble diamond in appearance and several properties. Special gemological techniques have been specially developed to tell apart natural and synthetic diamonds and diamond simulants.
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[edit] History
The name diamond is derived from the ancient Greek αδάμας (adámas), "proper", "unalterable", "unbreakable, untamed", from ἀ- (a-), "un-" + δαμάω (damáō), "I overpower, I tame". Diamonds are thought to possess been first recognized and mined in India, where significant alluvial deposits from the stone could be found many centuries ago across the rivers Penner, Krishna and Godavari. Diamonds happen to be known in India not less than 3,000 years but most likely 6,000 years.
Diamonds have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early history. The recognition of diamonds has risen because the 1800s because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns.
In 1772, Antoine Lavoisier used a lens to concentrate the sun's rays on the diamond within an atmosphere of oxygen, and demonstrated that the only real product from the combustion was co2, proving that diamond is composed of carbon. Later in 1797, Smithson Tennant repeated and expanded that experiment. By demonstrating that burning diamond and graphite releases the same amount of gas he established the chemical equivalence of those substances.
The most familiar use of diamonds today is as gemstones used for adornment, a use which dates back into antiquity. The dispersion of white light into spectral colors is the primary gemological sign of gem diamonds. In the Twentieth century, experts in gemology have developed methods of grading diamonds along with other gemstones based on the characteristics most important for their value like a gem. Four characteristics, known informally since the four Cs, are now commonly used since the basic descriptors of diamonds: they are carat, cut, color, and clarity. A large, flawless diamond is known as a paragon.
[edit] Material properties
A diamond is a transparent crystal of tetrahedrally bonded carbon atoms (sp3) that crystallizes to the diamond lattice which is a variation of the face centered cubic structure. Diamonds have been adapted for a lot of uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity (900-2,320 W·m-1·K-1), in addition to wide bandgap and high optical dispersion. Above 1,700 °C (1,973 K / 3,583 °F) in vacuum or oxygen-free atmosphere, diamond converts to graphite; in air, transformation starts at ~700 °C. Natural diamonds possess a density ranging from 3.15-3.53 g/cm3, with pure diamond close to 3.52 g/cm3. Caffeine bonds that contain the carbon atoms in diamonds together are weaker compared to those in graphite. In diamonds, the bonds form an inflexible three-dimensional lattice, whereas in graphite, the atoms are tightly bonded into sheets, which could slide easily over one another, making the overall structure weaker
[edit] Hardness
Diamond is the hardest natural material known, where hardness is understood to be potential to deal with scratching and it is graded between 1 (softest) and 10 (hardest) while using Mohs scale of mineral hardness. Diamond has a hardness of 10 (hardest) on this scale. Diamond's hardness continues to be known since antiquity, and it is the source of its name.
Diamond hardness depends on its purity, crystalline perfection and orientation: hardness is higher for flawless, pure crystals oriented to the <111> direction (along the longest diagonal from the cubic diamond lattice). Therefore, whereas it might be possible to scratch some diamonds along with other materials, such as boron nitride, the hardest diamonds are only able to be scratched by other diamonds and nanocrystalline diamond aggregates.
The hardness of diamond plays a role in its suitability like a gemstone. Because it are only able to be scratched by other diamonds, it maintains its polish extremely well. Unlike a number of other gems, it's well-suited to daily wear because of its resistance to scratching-perhaps adding to its popularity since the preferred gem in engagement or wedding rings, which are generally worn every single day.
The hardest natural diamonds mostly result from the Copeton and Bingara fields located in the New England area in New South Wales, Australia. These diamonds are generally small, perfect to semiperfect octahedra, and therefore are used to polish other diamonds. Their hardness is associated with the crystal growth form, which is single-stage crystal growth. Other diamonds show more proof of multiple growth stages, which produce inclusions, flaws, and defect planes within the crystal lattice, all of which affect their hardness. It is possible to treat regular diamonds within mixture of high pressure and temperature to create diamonds that are harder compared to diamonds used in hardness gauges.
Somewhat related to hardness is another mechanical property toughness, the industry material's ability to resist breakage from forceful impact. The toughness of natural diamond continues to be measured as 7.5-10 MPa·m1/2. This value is good compared to other gemstones, but poor compared to most engineering materials. As with any material, the macroscopic geometry of the diamond plays a role in its potential to deal with breakage. Diamond includes a cleavage plane and it is therefore more fragile in certain orientations than others. Diamond cutters make use of this attribute to cleave some stones, prior to faceting
[edit] Electrical conductivity
Other specialized applications also exist or are now being developed, including use as semiconductors: some blue diamonds are natural semiconductors, in contrast to most diamonds, which are excellent electrical insulators. The conductivity and blue color originate from boron impurity. Boron substitutes for carbon atoms within the diamond lattice, donating an opening to the valence band.
Substantial conductivity is commonly seen in nominally undoped diamond grown by chemical vapor deposition. This conductivity is assigned to hydrogen-related species adsorbed in the surface, and it can be removed by annealing or other surface treatments
[edit] Color
Diamond includes a wide bandgap of 5.5 eV corresponding to the deep ultraviolet wavelength of 225 nanometers. What this means is pure diamond should transmit visible light and appear as a clear colorless crystal. Colors in diamond originate from lattice defects and impurities. Diamonds crystal lattice is exceptionally strong in support of atoms of nitrogen, boron and hydrogen can be introduced into diamond throughout the growth at significant concentrations (up to atomic percents). Transition metals Ni and Co, which are popular for development of synthetic diamond by high-pressure high-temperature techniques, have been detected in diamond as individual atoms; the maximum concentration is 0.01% for Ni and even much less for Co. Virtually any element could be introduced to diamond by ion implantation.
Nitrogen is in no way the most typical impurity present in gem diamonds and is accountable for the yellow and brown color in diamonds. Boron is responsible for the blue color. Color in diamond has two additional sources: irradiation (usually by alpha particles), that causes the colour in green diamonds; and plastic deformation of the diamond crystal lattice. Plastic deformation may be the cause of color in some brown and maybe pink and red diamonds. In order of rarity, yellow diamond is then brown, colorless, then by blue, green, black, pink, orange, purple, and red. "Black", or Carbonado, diamonds are not truly black, but instead contain numerous dark inclusions giving the gems their dark appearance. Colored diamonds contain impurities or structural defects that create the coloration, while pure or nearly pure diamonds are transparent and colorless. Most diamond impurities replace a carbon atom within the crystal lattice, known as the carbon flaw. The most typical impurity, nitrogen, leads to a slight to intense yellow coloration based upon the kind and power of nitrogen present. The Gemological Institute of America (GIA) classifies low saturation yellow and brown diamonds as diamonds within the normal color range, and applies a grading scale from "D" (colorless) to "Z" (light yellow). Diamonds of a different color, such as blue, are called fancy colored diamonds, and fall under another grading scale
In 2008, the Wittelsbach Diamond, a 35.56-carat (7.11 g) blue diamond once of the King of Spain, fetched over US$24 million in a Christie's auction. In May 2009, a 7.03-carat (1.41 g) blue diamond fetched the greatest price per carat ever paid for diamond jewelry when it had been sold at auction for 10.5 million Swiss francs (6.97 million euro or US$9.5 million at the time). That record was however beaten the same year: a 5-carat (1.0 g) vivid pink diamond was sold for $10.8 million in Hong Kong on December 1, 2009
[edit] Identification
Diamonds can be identified by their high thermal conductivity. Their high refractive index is also indicative, but many other materials have similar refractivity. Diamonds cut glass, but this doesn't positively identify a diamond because many other materials, for example quartz, also lie above glass about the Mohs scale and may also cut it. Diamonds can scratch other diamonds, but this can result in harm to either stones. Hardness tests are infrequently utilized in practical gemology because of their potentially destructive nature. The ultimate hardness and quality value of diamond means that gems are usually polished slowly using painstaking traditional techniques and greater focus on detail than is the situation with most other gemstones; these tend to lead to extremely flat, highly polished facets with exceptionally sharp facet edges. Diamonds also possess an extremely high refractive index and fairly high dispersion. Taken together, these factors get a new overall look of the polished diamond and many diamantaires still rely upon skilled utilization of a loupe (magnifying glass) to recognize diamonds 'by eye'
[edit] Synthetic diamonds
Diamonds are formed from carbon crystallized by extreme pressures deep within the Earth's mantle. Interestingly, they are also sometimes found at the site of a meteor impact. The conditions that forge diamonds over long periods of time underground also occur in the instant of impact between Earth and meteor. With technology advancement, scientists have also been able to create diamonds synthetically.
The Gemological Institute of America (GIA) recognizes synthetic diamonds as real from a compositional perspective. But, the man-made diamonds don't have the rich geological history that natural diamonds do. Laboratories simulate the heat and pressure from the Earth's mantle that create natural diamonds. For the synthetic manufacturers and the consumers, diamonds come down to a matter of time and money: days versus millions of years, man-made diamonds sell for about 30 percent less than natural ones.
[edit] Cubic zirconia
Cubic zirconia, commonly called CZ, is a laboratory gem that has been on the market since 1976. It's a hard gem (8.5 on the Mohs Scale), but it's not as hard as diamond. On the one hand, CZ is compositionally superior to diamond. CZ has greater brilliance and sparkle, it's entirely colorless and it has no inclusions.
[edit] Moissanite
Moissanite has become CZ's biggest synthetic rival. Moissanite became available in 1998, and it's even more similar to diamond in composition and appearance. Moissanite is harder than CZ, but at 9.5 on the Mohs Scale, it is still softer than diamond. Moissanite's color is faintly yellow or green, and the tint becomes more apparent in larger stones. It also has small, stretch-mark-like inclusions that form during its growing process.
[edit] Environmental Impact
Large areas of land and surrounding ecosystems can be disturbed as well as the potential for acid mine drainage causing damage to an ecosystem.
Environmental reclamation surrounding diamond mining operations generally involves some effort to return the altered landscape back to its original shape. This includes not only saving the fill removed from the pit and refilling pits once mining has ceased, but also preserving topsoil to be re-deposited on reclaimed land so that vegetation can be planted. In addition, diamond mining faces challenges relating to energy use and emissions which can contribute to the global climate change.
