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Monday, April 20, 2009
The Unique Properties of Diamonds
The diamond is the best known and the most heavily marketed gemstone. Like graphite, lonsdaleite ("hexagonal diamond"), and the fullerenes, a diamond is an allotrope of carbon and, no matter what its size, each diamond can be considered to be a single molecule of carbon.
Diamond is the hardest natural substance (while carbon is one of the softest). The word diamond derives from Greek adamas or "hardest steel". Pliny the Elder (A.D. 23 to 79) wrote that "the best way to test adamas is upon the anvil; strike even upon the point of the adamas with a hammer as hard as you can, it defies all blows and instead of the stone yielding, the hammer flies into pieces and even the anvil splits in half." This experiment, however, is not recommended: though hard, a diamond is brittle, and can crack under the shock of a sudden, sharp blow.
Diamond has an isometric crystallography. The crystal structure of a diamond, called a face centered cubic lattice, derives from the way each carbon atom joins four other carbon atoms in regular tetrahedrons (triangular prisms). It is possible to cleave, or split, a diamond, along its crystal face (grain), such that each side of the cleavage remains smooth.
The adamantine luster (the brilliance and "fire") of a diamond is due to its high dispersion and its high refractive index (a measure of how far it can bend light). Commercial gem diamonds are colorless or pale, steely blue. Strongly colored gem diamonds, called "fancies," are extremely rare and valuable (especially red, pink, and blue). Diamonds can also be gray, yellow, brown, green, orange, lavender, and even black. Diamond crystals frequently contain inclusions of other minerals. Many diamonds fluoresce blue to violet and the effect is sometimes strong enough to be seen in daylight. Some blue-fluorescing diamonds phosphoresce yellow (afterglow reaction).
Diamond has a high specific gravity. A diamond does not conduct electricity well (it is a semiconductor), but conducts heat extremely well. At a high enough temperature in the presence of oxygen, diamond can burn.
Composition and color
Diamonds occur in a restricted variety of colors — black, brown, yellow, gray, white, blue, orange, purple to pink, red, and chartreuse. Colored diamonds contain crystallographic defects, including substitutional impurities and structural defects, that cause the coloration. Theoretically, pure diamonds would be transparent and colorless. Diamonds are scientifically classed into two main types and several subtypes, according to the nature of defects present and how they affect light absorption:
Type I diamond has nitrogen (N) atoms as the main impurity, at a concentration of up to 1 percent. If the N atoms are in pairs they do not affect the diamond's color; these are Type IaA. If the N atoms are in larger aggregates they impart a yellow to brown tint (Type IaB); the yellow color mostly originates from 3-nitrogen complexes (N3 center). About 98 percent of gem diamonds are type Ia, and most of these are a mixture of IaA and IaB material: these diamonds belong to the Cape series, named after the diamond-rich region formerly known as Cape Province in South Africa, whose deposits are largely Type Ia. If the N atoms are dispersed throughout the crystal in isolated sites (not paired or grouped), they give the stone an intense yellow or occasionally brown tint (Type Ib); the rare canary diamonds belong to this type, which represents only one per thousand of known natural diamonds. Synthetic diamond containing nitrogen is usually type Ib. Type I diamonds absorb in both the infrared and ultraviolet region, from 320 nm. They also have a characteristic fluorescence and visible absorption spectrum (see Optical properties).
Type II diamonds have very few if any nitrogen impurities. Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising through plastic deformation during crystal growth[21] — these diamonds are rare (1.8 percent of gem diamonds), but constitute a large percentage of Australian production. Type IIb diamonds, which account for 0.1 percent of gem diamonds, are usually a steely blue or gray due to scattered boron within the crystal matrix; these diamonds are also semiconductors, unlike other diamond types (see Electrical properties). Most blue-gray diamonds coming from the Argyle mine of Australia are not of type IIb, but of Ia type. Those diamonds contain large concentrations of defects and impurities (especially hydrogen and nitrogen) and the origin of their color is yet uncertain[11]. Type II diamonds absorb in a different region of the infrared (which absorption is due to the diamond lattice rather than impurities), and transmit in the ultraviolet below 225 nm, unlike type I diamonds. They also have differing fluorescence characteristics, but no discernible visible absorption spectrum.
Certain diamond enhancement techniques are commonly used to artificially produce an array of colors, including blue, green, yellow, red, and black. Color enhancement techniques usually involve irradiation, including proton and deuteron bombardment via cyclotrons; neutron bombardment via the piles of nuclear reactors; and electron bombardment via Van de Graaff generators. These high-energy particles physically alter the diamond's crystal lattice, knocking carbon atoms out of place and producing color centers. The depth of color penetration depends on the technique and its duration, and in some cases the diamond may be left radioactive to some degree.
It should be noted that some irradiated diamonds are completely natural—one famous example is the Dresden Green Diamond. In these natural stones the color is imparted by "radiation burns" (natural irradiation by alpha particles originating from uranium ore) in the form of small patches, usually only skin deep. Additionally, Type IIa diamonds can have their structural deformations "repaired" via a high-pressure high-temperature (HPHT) process, removing much or all of the diamond's color.
Type I diamond has nitrogen (N) atoms as the main impurity, at a concentration of up to 1 percent. If the N atoms are in pairs they do not affect the diamond's color; these are Type IaA. If the N atoms are in larger aggregates they impart a yellow to brown tint (Type IaB); the yellow color mostly originates from 3-nitrogen complexes (N3 center). About 98 percent of gem diamonds are type Ia, and most of these are a mixture of IaA and IaB material: these diamonds belong to the Cape series, named after the diamond-rich region formerly known as Cape Province in South Africa, whose deposits are largely Type Ia. If the N atoms are dispersed throughout the crystal in isolated sites (not paired or grouped), they give the stone an intense yellow or occasionally brown tint (Type Ib); the rare canary diamonds belong to this type, which represents only one per thousand of known natural diamonds. Synthetic diamond containing nitrogen is usually type Ib. Type I diamonds absorb in both the infrared and ultraviolet region, from 320 nm. They also have a characteristic fluorescence and visible absorption spectrum (see Optical properties).
Type II diamonds have very few if any nitrogen impurities. Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising through plastic deformation during crystal growth[21] — these diamonds are rare (1.8 percent of gem diamonds), but constitute a large percentage of Australian production. Type IIb diamonds, which account for 0.1 percent of gem diamonds, are usually a steely blue or gray due to scattered boron within the crystal matrix; these diamonds are also semiconductors, unlike other diamond types (see Electrical properties). Most blue-gray diamonds coming from the Argyle mine of Australia are not of type IIb, but of Ia type. Those diamonds contain large concentrations of defects and impurities (especially hydrogen and nitrogen) and the origin of their color is yet uncertain[11]. Type II diamonds absorb in a different region of the infrared (which absorption is due to the diamond lattice rather than impurities), and transmit in the ultraviolet below 225 nm, unlike type I diamonds. They also have differing fluorescence characteristics, but no discernible visible absorption spectrum.
Certain diamond enhancement techniques are commonly used to artificially produce an array of colors, including blue, green, yellow, red, and black. Color enhancement techniques usually involve irradiation, including proton and deuteron bombardment via cyclotrons; neutron bombardment via the piles of nuclear reactors; and electron bombardment via Van de Graaff generators. These high-energy particles physically alter the diamond's crystal lattice, knocking carbon atoms out of place and producing color centers. The depth of color penetration depends on the technique and its duration, and in some cases the diamond may be left radioactive to some degree.
It should be noted that some irradiated diamonds are completely natural—one famous example is the Dresden Green Diamond. In these natural stones the color is imparted by "radiation burns" (natural irradiation by alpha particles originating from uranium ore) in the form of small patches, usually only skin deep. Additionally, Type IIa diamonds can have their structural deformations "repaired" via a high-pressure high-temperature (HPHT) process, removing much or all of the diamond's color.
Thermal stability
Being a form of carbon, diamond graphitizes in the presence of oxygen if heated over 800 °C (1500 °F). In absence of oxygen, e.g. in a flow of high-purity Ar gas, diamond can be heated up to ~1700 °C[18][19]. Its surface blackens, but can be recovered by re-polishing. At high pressure (~20 GPa) diamond can be heated up to 2500 °C[20] and recent unpublished reports reveal that diamond can withstand ~3000 °C.
In the late 18th century, diamonds were demonstrated to be made of carbon by the rather expensive experiment of igniting a diamond (by means of a burning-glass) in an oxygen atmosphere and showing that carbonic acid gas (carbon dioxide) was the product of the combustion. The fact that diamonds are combustible bears further examination because it is related to an interesting fact about diamonds. Diamonds are carbon crystals that form deep within the Earth under high temperatures and extreme pressures. At surface air pressure (one atmosphere), diamonds are not as stable as graphite, and so the decay of diamond is thermodynamically favorable (δH = −2 kJ / mol). Diamonds had previously been shown to burn during Roman times.
So, despite De Beers' 1948 ad campaign, diamonds are definitely not forever. However, owing to a very large kinetic energy barrier, diamonds are metastable; they will not decay into graphite under normal conditions.[citation needed
In the late 18th century, diamonds were demonstrated to be made of carbon by the rather expensive experiment of igniting a diamond (by means of a burning-glass) in an oxygen atmosphere and showing that carbonic acid gas (carbon dioxide) was the product of the combustion. The fact that diamonds are combustible bears further examination because it is related to an interesting fact about diamonds. Diamonds are carbon crystals that form deep within the Earth under high temperatures and extreme pressures. At surface air pressure (one atmosphere), diamonds are not as stable as graphite, and so the decay of diamond is thermodynamically favorable (δH = −2 kJ / mol). Diamonds had previously been shown to burn during Roman times.
So, despite De Beers' 1948 ad campaign, diamonds are definitely not forever. However, owing to a very large kinetic energy barrier, diamonds are metastable; they will not decay into graphite under normal conditions.[citation needed
Thermal conductivity
Unlike most electrical insulators, diamond is a good conductor of heat because of the strong covalent bonding within the crystal. Most natural blue diamonds contain boron atoms which replace carbon atoms in the crystal matrix, and also have high thermal conductance. Monocrystalline synthetic diamond enriched in 12C isotope (99.9%) has the highest thermal conductivity of any known solid at room temperature: >30 W/cm·K [16] five times more than copper. Because diamond has such high thermal conductance it is already used in semiconductor manufacture to prevent silicon and other semiconducting materials from overheating. At lower temperatures conductivity becomes even better as its Fermi electrons can match the phononic normal transport mode near the Debye point,[17] and transport heat more swiftly, to reach ~800 W/cm·K at 100 K (12C enriched diamond)[16]
Diamond's thermal conductivity is made use of by jewelers and gemologists who may employ an electronic thermal probe to separate diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. This test takes about 2–3 seconds. However, older probes will be fooled by moissanite, a crystalline mineral form of silicon carbide introduced in 1998 as an alternative to diamonds, which has a similar thermal conductivity.
Diamond's thermal conductivity is made use of by jewelers and gemologists who may employ an electronic thermal probe to separate diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. This test takes about 2–3 seconds. However, older probes will be fooled by moissanite, a crystalline mineral form of silicon carbide introduced in 1998 as an alternative to diamonds, which has a similar thermal conductivity.
Electrical properties
Except for most natural blue diamonds—which are semiconductors due to substitutional boron impurities replacing carbon atoms—diamond is a good electrical insulator. Natural blue or blue-gray diamonds, common for the Argyle diamond mine in Australia, are rich in hydrogen; these diamonds are not semiconductors and it is unclear whether hydrogen is actually responsible for their blue-gray color.[11] Natural blue diamonds containing boron and synthetic diamonds doped with boron are p-type semiconductors. N-type diamond films are reproducibly synthesized by phosphorus doping during chemical vapor deposition. Diode p-n junctions and UV light emitting diodes (LEDs, at 235 nm) has been produced by sequential deposition of p-type (boron-doped) and n-type (phosphorus-doped) layers.[12]
Main article: covalent superconductors
In April 2004 Nature reported that below the superconducting transition temperature 4 K, boron-doped diamond synthesized at high temperature and high pressure is a bulk, type-II superconductor[13]. Superconductivity was later observed in heavily boron-doped films grown by various chemical vapor deposition techniques, and the highest reported transition temperature (by 2009) is 11.4 K [14][15].
Main article: covalent superconductors
In April 2004 Nature reported that below the superconducting transition temperature 4 K, boron-doped diamond synthesized at high temperature and high pressure is a bulk, type-II superconductor[13]. Superconductivity was later observed in heavily boron-doped films grown by various chemical vapor deposition techniques, and the highest reported transition temperature (by 2009) is 11.4 K [14][15].
Optical properties
The luster of a diamond is described as 'adamantine', which simply means diamond-like. It is the highest luster possible bar that of metal (metallic), and is due to diamond's superlative hardness. Reflections on a properly cut diamond's facets are undistorted, due to their flatness. The refractive index of diamond (as measured via sodium light, 589.3 nm) is 2.417; because it is cubic in structure, diamond is also isotropic. Its high dispersion of 0.044 (B-G interval) manifests in the perceptible fire of cut diamonds. This fire—flashes of prismatic colors seen in transparent stones—is perhaps diamond's most important optical property from a jewelry perspective. The prominence or amount of fire seen in a stone is heavily influenced by the choice of diamond cut and its associated proportions (particularly crown height), although the body color of fancy diamonds may hide their fire to some degree.
Note that many other minerals have higher dispersion than diamond: sphene 0.051, andradite 0.057, cassiterite 0.071, SrTiO3 0.109, sphalerite 0.156, synthetic rutile 0.330 ![5] However the combination of dispersion with extreme hardness, wear and chemical resistivity, as well as clever marketing, determines the exceptional value of diamond as a gemstone.
Diamonds exhibit fluorescence of various colors and intensities under long wave (LW) ultra-violet light (365 nm): Cape series stones (type Ia; see composition and color) usually fluoresce blue, and these stones may also phosphoresce yellow. (This is a unique property among gemstones). Other LW fluorescence colors possible are green (usually in brown stones), yellow, mauve, or red (type IIb) [6]. In natural diamonds there is typically little if any response to shortwave (SW) ultraviolet, but the reverse is true of synthetics. Some natural type IIb diamonds phosphoresce blue after exposure to SW ultraviolet. In naturals, fluorescence under X-rays is generally bluish-white, yellowish or greenish. Some diamonds, particularly Canadian diamonds, show no fluorescence.
The origin of those luminescence colors is often unclear and not unique. Blue emission from type IIa and IIb diamonds is reliably identified with dislocations by directly correlating the emission with dislocations in an electron microscope.[7] However, blue emission in type Ia diamond could be either due to dislocations or the N3 defects (three nitrogen atoms bordering a vacancy)[8]. Green emission in type Ia diamond is usually due to the H3 center (two substitutional nitrogen atoms separated by a vacancy)[9]. Orange or red emission could be due to various reasons, one being the nitrogen-vacancy center which is present in sufficient quantities in all types of diamond, even type IIb.
Cape series diamonds have a visible absorption spectrum (as seen through a direct-vision spectroscope) consisting of a fine line in the violet at 415.5 nm—however, this line is often invisible until the diamond has been cooled to very low temperatures. Associated with this are weaker lines at 478 nm (often only this line is visible), 465 nm, 452 nm, 435 nm, and 423 nm. All those lines are labeled as N3 and N2 optical centers and associated with a defect consisting of three nitrogen atoms bordering a vacancy. Other stones show additional bands: brown, green, or yellow diamonds show a band in the green at 504 nm (H3 center, see above), sometimes accompanied by two additional weak bands at 537 nm and 495 nm (H4 center, a large complex presumably involving 4 substitutional nitrogen atoms and 2 lattice vacancies[10]). Type IIb diamonds may absorb in the far red due to the substitutional boron, but otherwise show no observable visible absorption spectrum.
Gemological laboratories make use of spectrophotometer machines that can distinguish natural, artificial, and color-enhanced diamonds. The spectrophotometers analyze the infrared, visible, and ultraviolet absorption and luminescence spectra of diamonds cooled with liquid nitrogen to detect tell-tale absorption lines that are not normally discernible.
Note that many other minerals have higher dispersion than diamond: sphene 0.051, andradite 0.057, cassiterite 0.071, SrTiO3 0.109, sphalerite 0.156, synthetic rutile 0.330 ![5] However the combination of dispersion with extreme hardness, wear and chemical resistivity, as well as clever marketing, determines the exceptional value of diamond as a gemstone.
Diamonds exhibit fluorescence of various colors and intensities under long wave (LW) ultra-violet light (365 nm): Cape series stones (type Ia; see composition and color) usually fluoresce blue, and these stones may also phosphoresce yellow. (This is a unique property among gemstones). Other LW fluorescence colors possible are green (usually in brown stones), yellow, mauve, or red (type IIb) [6]. In natural diamonds there is typically little if any response to shortwave (SW) ultraviolet, but the reverse is true of synthetics. Some natural type IIb diamonds phosphoresce blue after exposure to SW ultraviolet. In naturals, fluorescence under X-rays is generally bluish-white, yellowish or greenish. Some diamonds, particularly Canadian diamonds, show no fluorescence.
The origin of those luminescence colors is often unclear and not unique. Blue emission from type IIa and IIb diamonds is reliably identified with dislocations by directly correlating the emission with dislocations in an electron microscope.[7] However, blue emission in type Ia diamond could be either due to dislocations or the N3 defects (three nitrogen atoms bordering a vacancy)[8]. Green emission in type Ia diamond is usually due to the H3 center (two substitutional nitrogen atoms separated by a vacancy)[9]. Orange or red emission could be due to various reasons, one being the nitrogen-vacancy center which is present in sufficient quantities in all types of diamond, even type IIb.
Cape series diamonds have a visible absorption spectrum (as seen through a direct-vision spectroscope) consisting of a fine line in the violet at 415.5 nm—however, this line is often invisible until the diamond has been cooled to very low temperatures. Associated with this are weaker lines at 478 nm (often only this line is visible), 465 nm, 452 nm, 435 nm, and 423 nm. All those lines are labeled as N3 and N2 optical centers and associated with a defect consisting of three nitrogen atoms bordering a vacancy. Other stones show additional bands: brown, green, or yellow diamonds show a band in the green at 504 nm (H3 center, see above), sometimes accompanied by two additional weak bands at 537 nm and 495 nm (H4 center, a large complex presumably involving 4 substitutional nitrogen atoms and 2 lattice vacancies[10]). Type IIb diamonds may absorb in the far red due to the substitutional boron, but otherwise show no observable visible absorption spectrum.
Gemological laboratories make use of spectrophotometer machines that can distinguish natural, artificial, and color-enhanced diamonds. The spectrophotometers analyze the infrared, visible, and ultraviolet absorption and luminescence spectra of diamonds cooled with liquid nitrogen to detect tell-tale absorption lines that are not normally discernible.
Toughness
Unlike hardness, which only denotes resistance to scratching, diamond's toughness or tenacity is only fair to good. Toughness relates to the ability to resist breakage from falls or impacts: due to diamond's perfect and easy cleavage, it is vulnerable to breakage. A diamond will shatter if hit with an ordinary hammer.
Ballas and carbonado diamond are exceptional, as they are polycrystalline and therefore much tougher than single-crystal diamond; they are used for deep-drilling bits and other demanding industrial applications. Particular cuts of diamonds are more prone to breakage—such as marquis or other cuts featuring tapered points—and thus may be uninsurable by reputable insurance companies. The culet is a facet (parallel to the table) given to the pavilion of cut diamonds designed specifically to reduce the likelihood of breakage or splintering. Extremely thin, or very thin girdles are also prone to much higher breakage.
Solid foreign crystals are commonly present in diamond—these and other inclusions, such as internal fractures or "feathers"—can compromise the structural integrity of a diamond. Cut diamonds that have been enhanced to improve their clarity via glass infilling of fractures or cavities are especially fragile, as the glass will not stand up to ultrasonic cleaning or the rigors of the jeweler's torch. Fracture-filled diamonds may shatter if treated improperly.
Ballas and carbonado diamond are exceptional, as they are polycrystalline and therefore much tougher than single-crystal diamond; they are used for deep-drilling bits and other demanding industrial applications. Particular cuts of diamonds are more prone to breakage—such as marquis or other cuts featuring tapered points—and thus may be uninsurable by reputable insurance companies. The culet is a facet (parallel to the table) given to the pavilion of cut diamonds designed specifically to reduce the likelihood of breakage or splintering. Extremely thin, or very thin girdles are also prone to much higher breakage.
Solid foreign crystals are commonly present in diamond—these and other inclusions, such as internal fractures or "feathers"—can compromise the structural integrity of a diamond. Cut diamonds that have been enhanced to improve their clarity via glass infilling of fractures or cavities are especially fragile, as the glass will not stand up to ultrasonic cleaning or the rigors of the jeweler's torch. Fracture-filled diamonds may shatter if treated improperly.
Hardness and crystal structure
Known to the ancient Greeks as adamas ("tame'sles" or "bridleless") and sometimes called adamant, diamond is the hardest known naturally occurring material, scoring 10 on the old Mohs scale of mineral hardness. The material boron nitride, when in a form structurally identical to diamond (zincblende structure), is nearly as hard as diamond; a currently hypothetical material, beta carbon nitride, may also be as hard or harder in one form. Furthermore, it has been shown[2][3] that nanocrystalline diamond powder (sometimes called aggregated diamond nanorods) is tougher than diamond, i.e. performs better as abrasive material. In turn, using those new ultrahard materials for diamond testing, more accurate values are now known for diamond hardness. A (111) surface (normal to the largest diagonal of a cube) of type IIa diamond has a hardness value of 167 GPa (±6) when scratched with an nanodiamond tip, while the nanodiamond sample itself has a value of 310 GPa when tested with a nanodiamond tip [2]. However, the test only works properly with a tip made of harder material than the sample being tested. This means that the true value for nanodiamond is likely somewhat lower than 310 GPa.
Cubic diamonds have a perfect and easy octahedral cleavage, which means that they have four planes—directions following the faces of the octahedron where there are fewer bonds and therefore points of structural weakness—along which diamond can easily split (following a blunt impact), leaving smooth surfaces. Similarly, diamond's hardness is markedly directional: the hardest direction is the diagonal on the cube face, 100 times harder than the softest direction, which is the dodecahedral plane. The octahedral plane, followed by the axial directions on the cube plane, are intermediate between the two extremes. The diamond cutting process relies heavily on this directional hardness, as without it a diamond would be nearly impossible to fashion. Cleavage also plays a helpful role, especially in large stones where the cutter wishes to remove flawed material or to produce more than one stone from the same piece of rough.
Diamonds crystallize in the diamond cubic crystal system (space group Fd\bar{3}m) and consist of tetrahedrally, covalently bonded carbon atoms. A second form called lonsdaleite with hexagonal symmetry is also found, but it is extremely rare and forms in meteorites or in laboratory synthesis. The local environment of each atom is identical in the two structures. In terms of crystal habit, diamonds occur most often as euhedral (well-formed) or rounded octahedra and twinned, flattened octahedra known as macles (with a triangular outline). Other forms include dodecahedra and (rarely) cubes. There is some evidence that nitrogen impurities play an important role in the formation of euhedral crystals—the largest diamonds found, such as the Cullinan Diamond, have been shapeless or massive. These diamonds are type II and therefore contain little if any nitrogen (see Composition and color).
Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in structure.
The faces of diamond octahedrons are highly lustrous due to their hardness; growth defects in the form of trigons or etch pits are often present on the faces, the former being triangular pits whose points are aligned with the faces of the octahedron. A diamond's fracture may be step-like, conchoidal (shell-like, similar to glass) or irregular. Diamonds which are nearly round due to the stepping tendency of octahedrons are commonly found coated in nyf, a gum-like skin; the combination of stepped faces, growth defects, and nyf produces a "scaly" or corrugated appearance, and such diamonds are termed crinkles. A significant number of diamonds crystallize anhedrally: that is, their forms are so distorted that few crystal faces are discernible. Some diamonds found in Brazil and the Democratic Republic of the Congo are cryptocrystalline and occur as opaque, darkly colored, spherical, radial masses of tiny crystals; these are known as ballas and are important to industry as they lack the cleavage planes of single-crystal diamond. Carbonado is a similar opaque microcrystalline form which occurs in shapeless masses. Like ballas diamond, carbonado lacks cleavage and its specific gravity varies widely, from 2.9–3.5. Bort diamonds, found in Brazil, Venezuela, and Guyana, are the most common type of industrial-grade diamond, also cryptocrystalline or otherwise poorly crystallized, but possessing cleavage, translucency, and lighter colors.
Due to its great hardness and strong molecular bonding, a cut diamond's facets and facet edges are observably the flattest and sharpest. A curious side effect of diamond's surface perfection is hydrophobia combined with lipophilia. The former property means a drop of water placed on a diamond will form a coherent droplet, whereas in most other minerals the water would spread out to cover the surface. Similarly, diamond is unusually lipophilic, meaning grease and oil readily collect on a diamond's surface. Whereas on other minerals oil would form coherent drops, on a diamond the oil would spread. This property is exploited in the use of so-called "grease pens," which apply a line of grease to the surface of a suspect diamond simulant. Diamond surfaces are hydrophobic when the surface carbon atoms terminate with a hydrogen atom and hydrophilic when the surface atoms terminate with an oxygen atom or hydroxyl radical. Treatment with gases or plasmas containing the appropriate gas, at temperatures of 450 C or higher, can change the surface property completely. Naturally occurring diamonds have a surface with less than a half monolayer coverage of oxygen, the balance being hydrogen and the behavior is moderately hydrophobic. This allows for separation from other minerals at the mine using the so-called "grease-belt".[4]
Diamond is so strong because of the shape the carbon atoms make. It's a very strong 3D shape, each carbon atom having four joined to it with covalent bonds.
Material properties of diamond
Diamond is transparent to opaque, optically isotropic, 3D-crystalline carbon. It is the hardest naturally occurring material known, owing to its strong covalent bonding, yet its toughness is only fair to good due to important structural weaknesses. The precise tensile strength of diamond is unknown. However, strength up to 60 GPa has been observed, and its theoretical intrinsic strength has been calculated as 90 to 225 GPa, depending on the crystal orientation.[1] Diamond has a high refractive index (2.417) and moderate dispersion (0.044), properties which are considered carefully during diamond cutting and which (together with their hardness) give cut diamonds their brilliance and fire. Scientists classify diamonds into two main types and several subtypes, depending on the nature of crystallographic defects present. Trace impurities substitutionally replacing carbon atoms in a diamond's crystal lattice, and in some cases structural defects, are responsible for the wide range of colors seen in diamond. Most diamonds are electrical insulators but extremely efficient thermal conductors. The specific gravity of single-crystal diamond (3.52) is fairly constant. Contrary to a common misconception, diamond is not the most stable form of solid carbon; graphite has that distinction.
How to Evaluate a Diamond Grading Certificate
A diamond grading certificate or report is like a "fingerprint" for the diamond, describing the stone in technical detail so that its value and identity can be verified. It does not assign monetary value to the stone, as an appraisal does, and is only provided for loose diamonds. If you are purchasing a diamond, it's important to ask for and know how to read a grading report so you can make sure you're getting what you pay for.
Tuesday, April 14, 2009
Silvermist Diamonds
Combining colours of morning mist with the twilight shades of night. Brilliant white and grey diamonds set in argentium silver, Silvermist Diamonds, unveil the mystery.
Birthstone
April
Brand
Silvermist Diamonds
Diamond
1/3 carat
Material
Silver
Stone setting
Pave
Stone shape
Round
Stone type
Diamond
A Historical Panorama: Diamond's Role in Adornment
Diamond's place in cultural history is explored through its presence in legend and mythology, as well as its role in art and adornment. Breathtaking jewelry and artifacts highlight the fascinating cultural and historical significance of diamond and show how diamond and its myths traveled from India to the West. The oldest cultural object in the exhibition, a Roman ring set with two rough diamonds, is dated from 300 A.D. A major cultural significance of diamond is reflected through the chronology of the diamond betrothal rings. A collection of five centuries of diamond betrothal rings, on loan from Benjamin Zucker, celebrates this tradition and demonstrates the evolution of diamond fashioning. On display from the middle ages, the Badge of the Order of the Garter is an important example of early use of diamonds in British royalty.
[Photo of a sampling of naturally colored diamonds from the Aurora Collection. On loan from Aurora Gems, Inc., New York. Photograph © Harold and Erica Van Pelt. The transition from "royal diamonds" to "everyone's diamonds" at the turn of the century is examined. Diamond's connotation of class, culture, and wealth captured the heart of Hollywood and is seen in a video of film clips and still photographs of diamond in Hollywood. Famous jewels of celebrities will be displayed in this area as well, including a diamond bracelet owned by Joan Crawford, an art deco shoulder brooch previously owned by Sir Elton John, and a ring worn by Ginger Rogers. Also included is a ring worn by Hillary Rodham Clinton at the 1993 and 1997 presidential inaugurals, a bracelet from the 17th Century owned by Mamie Doud Eisenhower, and pieces from New York fashion maven, Diana Vreeland.
A major highlight of the exhibit is the walk-in diamond vault, a high security, self-contained bank-style vault housing the most fabulous and notable diamonds of the exhibit. Among these are the 407.48-carat Incomparable (on loan from Zale Corporation, Dallas, Texas; Marvin Samuels, Premier Gem Corporation, New York; and Louis Glick, Co, New York); the Aurora collection, 260 naturally colored diamonds (on loan from Aurora Gems, New York); The Pumpkin Diamond, the largest fancy orange diamond ever recorded (on loan from Harry Winston); the Eureka, considered to be the "discovery diamond" that sparked a revolution in diamond production; and the Arkansas, an example of an exemplary diamond found in the U.S.
Of historic importance, the Cullinan Blue necklace created for Lady Annie Harding Cullinan, wife of Premier Mine owner, Sir Thomas Cullinan of South Africa. The Cullinan Blue is on loan courtesy of S. H. Silver Co., Inc., Menlo Park, California. The Tiffany bow corsage ornament is on display as well as an exquisite collection of tiaras from the 19th and 20th Centuries.
Diamond Exploration, Mining, and Marketing
The history of diamond exploration, mining and marketing is described in this part of the exhibit, detailing diamonds' transition from mine, to dealer, to their use in industry or as gems. Mining and exploration have extended to every continent but Antarctica, and have developed into a large, technically sophisticated diamond mining industry. Models will be on display that demonstrate the three types of mining: kimberlite pipe, or underground mining; alluvial, or gravel mining; and marine, or beach and undersea mining.
Visitors will get an inside look at the world of diamond exploration through "Diamonds in the Tundra," a video documentary following the fast-paced, high-priced exploration for diamonds ongoing in the Northwest Territories and Arctic reaches of Canada.
About Diamonds (Diamond FAQ)
The Four most popular factors used to
measure diamond quality are: Color, Carat,
Clarity and Cut. Topics to discuss are Diamond
Color Clarity Grade, Diamond Grades Quality Information & Diamond Grade Scale.
Diamond Color: Degree to which a diamond is colorless
Diamond Clarity: Presence of inclusions in a diamond
Diamond Carat: Weight of a diamond
Diamond Cut: Angles and proportions of a diamond
browse our exquisite DIAMOND JEWELRY
Diamond Jewelry
A Huge collection
of Gold Diamond Jewelry
in many styles.
Color: (The color used in this diagram is for presentation purposes and is not actual color.)
Many experts name color as the number one consideration in choosing a diamond. A diamond's color is graded on an alphabetical scale from D-Z, with D being absolutely colorless and Z being light yellow. Beyond "Z", a diamond is considered to be an exotic or "Fancy" color.
DIAMOND COLOR SCALE
D E F G H I J K L M N O P Q R S T U V W X Y Z
Colorless Near Colorless Faint Yellow Very Light Yellow Light Yellow
Since color differences can be so subtle, they are impossible to determine by the untrained eye. To grade a diamond, gemologists often place it on a white background next to another diamond that has been previously graded.
If all other factors are equal, the less color in a diamond or the higher color rating, the more valuable a diamond becomes. Likewise, as the amount of color increases, the price of a diamond decreases (though this does not necessarily reduce the beauty of a diamond.)
Clarity
All diamonds have identifying characteristics, but most are invisible to the naked eye. To view a diamond, experts use a 10x magnifying loupe which allows them to see the appearance of tiny crystals, feathers or clouds. These natural phenomena are called inclusions.There are five categories in class that anyone interested in purchasing a diamond should be aware of when grading clarity.
DIAMOND CLARITY SCALE
FL
IF
VVS1
VVS2
VS1
VS2
SI1
SI2
I1
I2
I3
Flawless-
Internally Flawless
Very Very Slightly
Imperfect
Very Slightly
Imperfect
Slightly Imperfect
Imperfect
FL (Flawless) - IF (Internally Flawless)
Flawless Diamonds reveal no flaws on the surface or internally are the rarest and most beautiful gems.
Internally Flawless Diamonds reveal no inclusions and only insignificant blemishes on the surface under 10x magnification.
VVS1 - VVS2 (Very, Very Slightly Included)
Very difficult to see inclusions under 10x magnification. These are excellent quality diamonds.
VS1 - VS2 (Very Slightly Included)
Only looking through a 10X loupe can pinpoint the inclusions in this category and are nearly impossible to see with the naked eye. These are less expensive than the VVS1 or VVS2 grades.
SI1 - SI3 (Slightly Included)
Diamonds with inclusions easily identified under 10x magnification. Finding flaws in this category with the naked eye is difficult. The gems in this category maintain their integrity, depending on the location of the inclusions.
I1 - I3 (Included)
Diamonds with inclusions which may or may not be easily seen by the naked eye. The flaws on the stones in this category will have some effect on the brilliance of your diamond.
Carat: (This diagram is for presentation purposes and is not to scale)
Carat is often confused with size even though it is a measure of weight. The cut of a diamond can make it appear larger or smaller than its actual weight.
One carat is the equivalent of 200 milligrams. One carat can be divided into 100 "points". A .75 carat diamond is the same as 75 points or a 3/4 carat diamond. Since larger diamonds are rarer than smaller diamonds, the value rises exponentially with carat weight.
Cut
Cut actually refers to two aspects of a diamond. The first is its shape (round, marquise, etc) the second is how well the cutting has been executed.
A diamond's cut will most certainly influence its fire (the lovely rainbow colors that flash from within) and brilliance (the liveliness and sparkle), as well as its perceived size and even, to some degree its apparent color. Different cuts reflect light in different angles. A diamond must be cut in a geometrically precise manner to maximize its brilliance.
Blue Diamonds
Fancy blue diamonds are available in a wide range of shades, from the blue of the sky to a more "steely" colour than sapphire.
Limited quantities of fancy blue diamonds are recovered from the Argyle mine
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