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For example, most white diamonds are discounted in price as a more yellow hue is detectable, while intense pink or blue diamonds such as the Hope Diamond can be dramatically more valuable.

The Aurora Diamond Collection displays a spectacular array of naturally colored diamonds, which occur in every color of the rainbow. Most diamonds used as gemstones are basically transparent with little tint, or white diamonds.

The GIA has developed a rating system for color in white diamonds, from D to Z with D being "colorless" and Z having a bright yellow coloration , which has been widely adopted in the industry and is universally recognized, superseding several older systems.

The GIA system uses a benchmark set of natural diamonds of known color grade, along with standardized and carefully controlled lighting conditions.

Diamonds with higher color grades are rarer, in higher demand, and therefore more expensive, than lower color grades.

Oddly enough, diamonds graded Z are also rare, and the bright yellow color is also highly valued. N—Y usually appear light yellow or brown.

In contrast to yellow or brown hues, diamonds of other colors are more rare and valuable. While even a pale pink or blue hue may increase the value of a diamond, more intense coloration is usually considered more desirable and commands the highest prices.

A variety of impurities and structural imperfections cause different colors in diamonds, including yellow, pink, blue, red, green, brown, and other hues.

Diamonds with unusual or intense coloration are sometimes labeled "fancy" in the diamond industry. Intense yellow coloration is considered one of the fancy colors, and is separate from the color grades of white diamonds.

Gemologists have developed rating systems for fancy colored diamonds, but they are not in common use because of the relative rarity of such diamonds.

Diamond cutting is the art and science of creating a gem-quality diamond out of mined rough. The cut of a diamond describes the manner in which a diamond has been shaped and polished from its beginning form as a rough stone to its final gem proportions.

The cut of a diamond describes the quality of workmanship and the angles to which a diamond is cut. Often diamond cut is confused with "shape".

There are mathematical guidelines for the angles and length ratios at which the diamond is supposed to be cut in order to reflect the maximum amount of light.

Round brilliant diamonds, the most common, are guided by these specific guidelines, though fancy cut stones are not able to be as accurately guided by mathematical specifics.

The techniques for cutting diamonds have been developed over hundreds of years, with perhaps the greatest achievements made in by mathematician and gem enthusiast Marcel Tolkowsky.

He developed the round brilliant cut by calculating the ideal shape to return and scatter light when a diamond is viewed from above.

The modern round brilliant has 57 facets polished faces , counting 33 on the crown the top half , and 24 on the pavilion the lower half. The girdle is the thin middle part.

The culet is the tiny point or facet at the bottom of the diamond. This should be a negligible diameter, otherwise light leaks out of the bottom.

However, a girdle is required in reality in order to prevent the diamond from easily chipping in the setting. The thick part of the girdle is normally about 1.

However, there is a small range in which the diamond can be considered "ideal". Such calculations show a slightly larger table percentage, and a trade-off between pavilion angle and crown angle.

Today, because of the relative importance of carat weight among buyers, many diamonds are often intentionally cut poorly to increase carat weight.

There is a financial premium for a diamond that weighs the desirable 1. Neither of these changes makes the diamond appear any larger, and both greatly reduce the sparkle of the diamond.

A poorly cut 1. The depth percentage is the overall quickest indication of the quality of the cut of a round brilliant. Another quick indication is the overall diameter.

Typically a round brilliant 1. Mathematically, the diameter in millimeters of a round brilliant should approximately equal to 6.

Diamonds do not show all of their beauty as rough stones; instead, they must be cut and polished to exhibit the characteristic fire and brilliance that diamond gemstones are known for.

Diamonds are cut into a variety of shapes that are generally designed to accentuate these features. Diamonds which are not cut into a round brilliant shape are known as "fancy cuts.

Newer cuts that have been introduced into the jewelry industry are the "cushion" "radiant" similar to princess cuts, but with rounded edges instead of square edges and Asscher cuts.

Many fancy colored diamonds are now being cut according to these new styles. Generally speaking, these "fancy cuts" are not held to the same strict standards as Tolkowsky-derived round brilliants and there are less specific mathematical guidelines of angles which determine a well-cut stone.

Cuts are influenced heavily by fashion: The princess cut is also popular amongst diamond cutters: The past decades have seen the development of new diamond cuts, often based on a modification of an existing cut.

Some of these include extra facets. These newly developed cuts are viewed by many as more of an attempt at brand differentiation by diamond sellers, than actual improvements to the state of the art.

The skill with which a diamond is cut determines its ability to reflect and refract light. A number of factors, including proportion, polish, symmetry , and the relative angles of various facets, are determined by the quality of the cut and can affect the performance of a diamond.

A diamond with facets cut only a few degrees out of alignment can result in a poorly performing stone. For a round brilliant cut, there is a balance between "brilliance" and "fire".

When a diamond is cut for too much "fire", it looks like a cubic zirconia , which gives off much more "fire" than real diamond.

A well-executed round brilliant cut should reflect light upwards and make the diamond appear white when viewed from the top. An inferior cut will produce a stone that appears dark at the center and in extreme cases the setting may be seen through the top of the diamond as shadows.

Several different theories on the "ideal" proportions of a diamond have been and continue to be advocated by various owners of patents on machines to view how well a diamond is cut.

These advocate a shift away from grading cut by the use of various angles and proportions toward measuring the performance of a cut stone.

A number of specially modified viewers and machines have been developed toward this end. Hearts and Arrows viewers test for the " hearts and arrows " characteristic pattern observable in stones exhibiting high symmetry and particular cut angles.

Closely related to Hearts and Arrows viewers is the ASET which tests for light leakage, light return, and proportions. Detractors, however, see these machines as marketing tools rather than scientific ones.

The GIA has developed a set of criteria for grading the cut of round brilliant stones that is now the standard in the diamond industry and is called Facetware.

The process of shaping a rough diamond into a polished gemstone is both an art and a science. The choice of cut is often decided by the original shape of the rough stone, location of the inclusions and flaws to be eliminated, the preservation of the weight, popularity of certain shapes amongst consumers and many other considerations.

Oddly shaped crystals such as macles are more likely to be cut in a fancy cut —that is, a cut other than the round brilliant—which the particular crystal shape lends itself to.

Since the per carat price of diamond shifts around key milestones such as 1. Some jewelry experts advise consumers to buy a 0.

In the gem trade, the term light performance is used to describe how well a polished diamond will return light to the viewer.

There are three light properties which are described in relation to light performance: Brilliance refers to the white light reflections from the external and internal facet surfaces.

Fire refers to the spectral colors which are produced as a result of the diamond dispersing the white light. Scintillation refers to the small flashes of light that are seen when the diamond, light source or the viewer is moved.

A diamond that is cut and polished to produce a high level of these qualities is said to be high in light performance.

The setting diamonds are placed in also affect the performance of light through a diamond. The three most commonly used settings are: Prong, Bezel, and Channel.

Prong settings are the most popular setting for diamond jewelry. In bezel settings the diamond or gemstone is completely surrounded by a rim of metal, which can be molded into any shape to accommodate the stone.

Used to set earrings, necklaces, bracelets, and rings, bezel settings can have open or closed backs, and generally can be molded to allow a lot of light to pass through.

Channel settings set the stones right next to each other with no metal separating them. This setting is mostly used in wedding and anniversary bands.

The outer ridge is then worked over the edges of the stones to create a smooth exterior surface. This also protects the girdle area of the stone.

About a third of all diamonds will glow under ultraviolet light, usually a blue color which may be noticeable under a black light or strong sunlight.

Other colors diamonds can fluoresce are green , yellow , and red but are very rare and are sometimes a combination of the colors such as blue-green or orange.

Some diamonds with "very strong" fluorescence can have a "milky" or "oily" look to them, but they are also very rare and are termed "overblues.

Since blue is a complementary color to yellow and can appear to cancel it out, strong blue fluorescence had especially better color appearance with lower color graded diamonds that have a slight yellowish tint such as I or J color but had little effect on the more colorless D, E and F color grades.

A clean diamond is more brilliant and fiery than the same diamond when it is "dirty". Dirt or grease on the top of a diamond reduces its luster. Even a thin film absorbs some light that could have been reflected to the viewer.

Colored dye or smudges can affect the perceived color of a diamond. Current practice is to clean a diamond thoroughly before grading its color.

Maintaining a clean diamond can sometimes be difficult as jewelry settings can obstruct cleaning, and oils, grease, and other hydrophobic materials adhere well to a diamond.

Many jewelers use steam cleaners. Some jewelers provide their customers with ammonia -based cleaning kits; ultrasonic cleaners are also popular.

Historically, it has been claimed that diamonds possess several supernatural powers:. Because of their extraordinary physical properties , diamonds have been used symbolically since near the time of their first discovery.

Perhaps the earliest symbolic use of diamonds was as the eyes of Hindu devotional statues. Vajra is the word for diamond and ayudham means weapon in Sanskrit.

Another name for it was Agira which means fire or the sun. In fact there are 14 names counted to be given to a diamond in traditional Hinduism.

The oldest dated printed book in the world is called the Diamond Sutra , a Chinese text dating from and was found in the Mogao Caves.

Sutras are most used to describe the teachings of Buddha. Jewel imagery forms a central part of Buddhism: The book presently resides in the British Library.

Many cultures use divine intervention to explain the origin and creation of gemstones, and diamonds were no exception to this. In Greek mythology for example it was the youth on the island of Crete that disturbed Zeus and who were then as a form of punishment transformed into the adamas.

Philosophers however had a more naturalistic approach to explain the origin of gems: Plato for example believed gemstones were a consequence of fermentation in the stars, where a diamond actually formed the kernel of gold-bearing mass.

In later times, Robert Boyle actually believed that gems including a diamond were formed of clear, transparent water, and that their colors and characteristics were derived from their metallic spirit.

The diamond is the birthstone for people born in the month of April, and is also used as the symbol of a sixty-year anniversary , such as a Diamond Jubilee see hierarchy of precious substances.

In a system of heraldry by gemstone occasionally used in the past for the arms of nobles, diamond was used to represent the color sable, or black.

The origin of the custom to use diamonds in rings, and more recently, in engagement rings , can be traced back to the Middle Ages and even the Romans.

The Romans valued the diamond entirely on account of the supernatural powers they ascribed to it. In subduction zones, which are colder, it becomes stable at temperatures of degrees C and pressures of 3.

At depths greater than km, iron-nickel metal phases are present and carbon is likely to be either dissolved in them or in the form of carbides. Thus, the deeper origin of some diamonds may reflect unusual growth environments.

In the first known natural samples of a phase of ice called Ice VII were found as inclusions in diamond samples.

The inclusions formed at depths between and km, straddling the upper and lower mantle, and provide evidence for water-rich fluid at these depths.

The amount of carbon in the mantle is not well constrained, but its concentration is estimated at 0. This ratio has a wide range in meteorites, which implies that it was probably also broad in the early Earth.

It can also be altered by surface processes like photosynthesis. This variability implies that they are not formed from carbon that is primordial having resided in the mantle since the Earth formed.

Instead, they are the result of tectonic processes, although given the ages of diamonds not necessarily the same tectonic processes that act in the present.

Diamonds in the mantle form through a metasomatic process where a C-O-H-N-S fluid or melt dissolves minerals in a rock and replaces them with new minerals.

Diamonds form from this fluid either by reduction of oxidized carbon e. Using probes such as polarized light, photoluminescence and cathodoluminescence , a series of growth zones can be identified in diamonds.

The characteristic pattern in diamonds from the lithosphere involves a nearly concentric series of zones with very thin oscillations in luminescence and alternating episodes where the carbon is resorbed by the fluid and then grown again.

Diamonds from below the lithosphere have a more irregular, almost polycrystalline texture, reflecting the higher temperatures and pressures as well as the transport of the diamonds by convection.

Geological evidence supports a model in which kimberlite magma rose at 4—20 meters per second, creating an upward path by hydraulic fracturing of the rock.

As the pressure decreases, a vapor phase exsolves from the magma, and this helps to keep the magma fluid. Then, at lower pressures, the rock is eroded, forming a pipe and producing fragmented rock breccia.

As the eruption wanes, there is pyroclastic phase and then metamorphism and hydration produces serpentinites.

Although diamonds on Earth are rare, they are very common in space. In meteorites , about three percent of the carbon is in the form of nanodiamonds , having diameters of a few nanometers.

Sufficiently small diamonds can form in the cold of space because their lower surface energy makes them more stable than graphite. The isotopic signatures of some nanodiamonds indicate they were formed outside the Solar System in stars.

High pressure experiments predict that large quantities of diamonds condense from methane into a "diamond rain" on the ice giant planets Uranus and Neptune.

Diamonds may exist in carbon-rich stars, particularly white dwarfs. One theory for the origin of carbonado , the toughest form of diamond, is that it originated in a white dwarf or supernova.

The most familiar uses of diamonds today are as gemstones used for adornment , and as industrial abrasives for cutting hard materials.

The markets for gem-grade and industrial-grade diamonds value diamonds differently. The dispersion of white light into spectral colors is the primary gemological characteristic of gem diamonds.

In the 20th century, experts in gemology developed methods of grading diamonds and other gemstones based on the characteristics most important to their value as a gem.

Four characteristics, known informally as the four Cs , are now commonly used as the basic descriptors of diamonds: A large, flawless diamond is known as a paragon.

A large trade in gem-grade diamonds exists. Although most gem-grade diamonds are sold newly polished, there is a well-established market for resale of polished diamonds e.

One hallmark of the trade in gem-quality diamonds is its remarkable concentration: One contributory factor is the geological nature of diamond deposits: Secondary alluvial diamond deposits, on the other hand, tend to be fragmented amongst many different operators because they can be dispersed over many hundreds of square kilometers e.

As a part of reducing its influence, De Beers withdrew from purchasing diamonds on the open market in and ceased, at the end of , purchasing Russian diamonds mined by the largest Russian diamond company Alrosa.

Botswana, Namibia, South Africa and Canada. Further down the supply chain, members of The World Federation of Diamond Bourses WFDB act as a medium for wholesale diamond exchange, trading both polished and rough diamonds.

Recently, diamond cutting centers have been established in China, India, Thailand , Namibia and Botswana. The recent expansion of this industry in India, employing low cost labor, has allowed smaller diamonds to be prepared as gems in greater quantities than was previously economically feasible.

Diamonds prepared as gemstones are sold on diamond exchanges called bourses. There are 28 registered diamond bourses in the world. Diamonds can be sold already set in jewelry, or sold unset "loose".

Mined rough diamonds are converted into gems through a multi-step process called "cutting". Diamonds are extremely hard, but also brittle and can be split up by a single blow.

Therefore, diamond cutting is traditionally considered as a delicate procedure requiring skills, scientific knowledge, tools and experience.

Its final goal is to produce a faceted jewel where the specific angles between the facets would optimize the diamond luster, that is dispersion of white light, whereas the number and area of facets would determine the weight of the final product.

For example, the diamond might be intended for display or for wear, in a ring or a necklace, singled or surrounded by other gems of certain color and shape.

Some of them are special, produced by certain companies, for example, Phoenix , Cushion , Sole Mio diamonds, etc. The most time-consuming part of the cutting is the preliminary analysis of the rough stone.

It needs to address a large number of issues, bears much responsibility, and therefore can last years in case of unique diamonds. The following issues are considered:.

After initial cutting, the diamond is shaped in numerous stages of polishing. Unlike cutting, which is a responsible but quick operation, polishing removes material by gradual erosion and is extremely time consuming.

The associated technique is well developed; it is considered as a routine and can be performed by technicians. Those flaws are concealed through various diamond enhancement techniques, such as repolishing, crack filling, or clever arrangement of the stone in the jewelry.

Remaining non-diamond inclusions are removed through laser drilling and filling of the voids produced. And the firm created new markets in countries where no diamond tradition had existed before.

De Beers still advertises diamonds, but the advertising now mostly promotes its own brands, or licensed product lines, rather than completely "generic" diamond products.

Brown-colored diamonds constituted a significant part of the diamond production, and were predominantly used for industrial purposes. They were seen as worthless for jewelry not even being assessed on the diamond color scale.

After the development of Argyle diamond mine in Australia in , and marketing, brown diamonds have become acceptable gems.

Industrial diamonds are valued mostly for their hardness and thermal conductivity, making many of the gemological characteristics of diamonds, such as the 4 Cs , irrelevant for most applications.

The boundary between gem-quality diamonds and industrial diamonds is poorly defined and partly depends on market conditions for example, if demand for polished diamonds is high, some lower-grade stones will be polished into low-quality or small gemstones rather than being sold for industrial use.

Within the category of industrial diamonds, there is a sub-category comprising the lowest-quality, mostly opaque stones, which are known as bort.

Industrial use of diamonds has historically been associated with their hardness, which makes diamond the ideal material for cutting and grinding tools.

As the hardest known naturally occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds.

Common industrial applications of this property include diamond-tipped drill bits and saws, and the use of diamond powder as an abrasive.

Less expensive industrial-grade diamonds, known as bort, with more flaws and poorer color than gems, are used for such purposes.

Specialized applications include use in laboratories as containment for high-pressure experiments see diamond anvil cell , high-performance bearings , and limited use in specialized windows.

The high thermal conductivity of diamond makes it suitable as a heat sink for integrated circuits in electronics. The mining and distribution of natural diamonds are subjects of frequent controversy such as concerns over the sale of blood diamonds or conflict diamonds by African paramilitary groups.

Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care is required not to destroy larger diamonds, and then sorted by density.

Today, diamonds are located in the diamond-rich density fraction with the help of X-ray fluorescence , after which the final sorting steps are done by hand.

Before the use of X-rays became commonplace, [86] the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.

Historically, diamonds were found only in alluvial deposits in Guntur and Krishna district of the Krishna River delta in Southern India.

Diamond extraction from primary deposits kimberlites and lamproites started in the s after the discovery of the Diamond Fields in South Africa.

Most of these mines are located in Canada, Zimbabwe, Angola, and one in Russia. The Crater of Diamonds State Park in Arkansas is open to the public, and is the only mine in the world where members of the public can dig for diamonds.

Australia boasts the richest diamantiferous pipe, with production from the Argyle diamond mine reaching peak levels of 42 metric tons per year in the s.

In some of the more politically unstable central African and west African countries, revolutionary groups have taken control of diamond mines , using proceeds from diamond sales to finance their operations.

Diamonds sold through this process are known as conflict diamonds or blood diamonds. In response to public concerns that their diamond purchases were contributing to war and human rights abuses in central and western Africa, the United Nations , the diamond industry and diamond-trading nations introduced the Kimberley Process in This is done by requiring diamond-producing countries to provide proof that the money they make from selling the diamonds is not used to fund criminal or revolutionary activities.

Although the Kimberley Process has been moderately successful in limiting the number of conflict diamonds entering the market, some still find their way in.

This is a stringent tracking system of diamonds and helps protect the "conflict free" label of Canadian diamonds. Synthetic diamonds are diamonds manufactured in a laboratory, as opposed to diamonds mined from the Earth.

The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has been satisfied in large part by synthetic diamonds, which have been manufactured by various processes for more than half a century.

However, in recent years it has become possible to produce gem-quality synthetic diamonds of significant size. The majority of commercially available synthetic diamonds are yellow and are produced by so-called high-pressure high-temperature HPHT processes.

Other colors may also be reproduced such as blue, green or pink, which are a result of the addition of boron or from irradiation after synthesis.

Another popular method of growing synthetic diamond is chemical vapor deposition CVD. The growth occurs under low pressure below atmospheric pressure.

It involves feeding a mixture of gases typically 1 to 99 methane to hydrogen into a chamber and splitting them to chemically active radicals in a plasma ignited by microwaves , hot filament , arc discharge , welding torch or laser.

A diamond simulant is a non-diamond material that is used to simulate the appearance of a diamond, and may be referred to as diamante.

Cubic zirconia is the most common. The gemstone moissanite silicon carbide can be treated as a diamond simulant, though more costly to produce than cubic zirconia.

Both are produced synthetically. Diamond enhancements are specific treatments performed on natural or synthetic diamonds usually those already cut and polished into a gem , which are designed to better the gemological characteristics of the stone in one or more ways.

Coatings are increasingly used to give a diamond simulant such as cubic zirconia a more "diamond-like" appearance. One such substance is diamond-like carbon —an amorphous carbonaceous material that has some physical properties similar to those of the diamond.

Advertising suggests that such a coating would transfer some of these diamond-like properties to the coated stone, hence enhancing the diamond simulant.

Techniques such as Raman spectroscopy should easily identify such a treatment. Early diamond identification tests included a scratch test relying on the superior hardness of diamond.

This test is destructive, as a diamond can scratch another diamond, and is rarely used nowadays. Instead, diamond identification relies on its superior thermal conductivity.

Electronic thermal probes are widely used in the gemological centers 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: This test takes about two to three seconds.

Whereas the thermal probe can separate diamonds from most of their simulants, distinguishing between various types of diamond, for example synthetic or natural, irradiated or non-irradiated, etc.

Those techniques are also used for some diamonds simulants, such as silicon carbide, which pass the thermal conductivity test. Optical techniques can distinguish between natural diamonds and synthetic diamonds.

They can also identify the vast majority of treated natural diamonds. Several methods for identifying synthetic diamonds can be performed, depending on the method of production and the color of the diamond.

CVD diamonds can usually be identified by an orange fluorescence. Screening devices based on diamond type detection can be used to make a distinction between diamonds that are certainly natural and diamonds that are potentially synthetic.

Those potentially synthetic diamonds require more investigation in a specialized lab. Occasionally, large thefts of diamonds take place.

The gang broke through a perimeter fence and raided the cargo hold of a Swiss-bound plane. The gang have since been arrested and large amounts of cash and diamonds recovered.

The identification of stolen diamonds presents a set of difficult problems. Rough diamonds will have a distinctive shape depending on whether their source is a mine or from an alluvial environment such as a beach or river—alluvial diamonds have smoother surfaces than those that have been mined.

Determining the provenance of cut and polished stones is much more complex. The Kimberley Process was developed to monitor the trade in rough diamonds and prevent their being used to fund violence.

Before exporting, rough diamonds are certificated by the government of the country of origin. Some countries, such as Venezuela, are not party to the agreement.

The Kimberley Process does not apply to local sales of rough diamonds within a country. Diamonds may be etched by laser with marks invisible to the naked eye.

Lazare Kaplan , a US-based company, developed this method. However, whatever is marked on a diamond can readily be removed. Diamonds have been known in India for at least 3, years but most likely 6, 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 human history.

In , the French scientist Antoine Lavoisier used a lens to concentrate the rays of the sun on a diamond in an atmosphere of oxygen , and showed that the only product of the combustion was carbon dioxide , proving that diamond is composed of carbon.

From Wikipedia, the free encyclopedia. Allotrope of carbon often used as a gemstone. This article is about the mineral.

For the gemstone, see Diamond gemstone. The slightly misshapen octahedral shape of this rough diamond crystal in matrix is typical of the mineral.

Its lustrous faces also indicate that this crystal is from a primary deposit. Material properties of diamond. Crystallographic defects in diamond.

A round brilliant cut diamond set in a ring. Diamond cutting and Diamond cut. List of diamond mines and Exploration diamond drilling.

Kimberley Process , Blood diamond , and Child labour in the diamond industry. Gemology and Jewelry portal. Retrieved July 7, Handbook of carbon, graphite, diamond, and fullerenes: The physics of diamond.

Retrieved 31 October Reports on Progress in Physics. Laser ablation in liquids: Phase boundaries and electronic properties from first-principles theory".

Proceedings of the National Academy of Sciences. Holt, Rinehart and Winston. In Radovic, Ljubisa R. Chemistry and physics of carbon.

Their sources, descriptions and identification 5th ed. A Stable Isotope Perspective". Annual Review of Earth and Planetary Sciences. Diamond and Related Materials.

Retrieved October 28, Properties, Growth and Applications of Diamond. Institution of Engineering and Technology.

Innovative superhard materials and sustainable coatings for advanced manufacturing. Handbook of ceramic grinding and polishing.

The nature of diamonds. Retrieved 1 November Philosophical Transactions of the Royal Society A. Retrieved March 31, Retrieved May 13, Synthetic, Imitation and Treated Gemstones.

Society for Mining, Metallurgy, and Exploration. The Mantle and Core. Archived from the original PDF on October 21, Retrieved June 16, Geology and Earth Science News and Information.

Archived from the original on October 30, Retrieved June 29, The Christian Science Monitor. Retrieved August 30, A dictionary of geology and earth sciences 4th ed.

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