Abalone
Abalone is the American English variant of the Spanish name [Abulón] used for various species of shellfish (mollusks) from the Haliotidae family (genus Haliotis). The abalones belong to the large class of gastropods (Gastropoda). There is only one genus in the family Haliotidae, and about four to seven subgenera. The taxonomy is somewhat confused. The number of species range from about 100 to about 130 species (due to the occurrence of hybrids), characterized by a richly coloured (on the inside--the outside is rough and mostly brown) shell yielding mother-of-pearl. This is also commonly called ear-shell, in Guernsey ormer (Fr. ormier, for oreille de mer), perlemoen in South Africa and paua in New Zealand. Abalone is also prevalent in Australian and South African coastal waters and is highly valued. The meat of an abalone is also considered an expensive delicacy in SE Asia, although it has a high cholesterol content.

Amber
Amber is a fossil resin much used for the manufacture of ornamental objects. Although not mineralized it is sometimes considered and used as a gemstone. Most of the world's amber is in the range of 30–90 million years old.Amber is heterogeneous in composition, but consists of several resinous bodies more or less soluble in alcohol, ether and chloroform, associated with an insoluble bituminous substance. Amber is a macromolecule by free radical polymerization of several precursors in the labdane family, communic acid, cummunol and biformene [1]. Labdanes are tetrameric terpenes (C20H32) and trienes which means that the organic skeleton has three alkene groups available for polymerization. As amber matures over the years, more polymerization will take place as well as isomerization reactions, crosslinking and cyclization. The average composition of amber leads to the general formula C10H16O.

Aquamarine
Aquamarine (Lat. aqua marina, "water of the sea") is a gemstone-quality transparent variety of beryl, having a delicate blue or bluish-green colour, suggestive of the tint of sea-water. It's closely related to the emerald.It occurs at most localities which yield ordinary beryl, some of the finest coming from Russia. The gem-gravels of Ceylon contain aquamarine. Clear yellow beryl, such as occurs in Brazil, is sometimes called aquamarine chrysolite. When corundum presents the bluish tint of typical aquamarine, it is often termed Oriental aquamarine.In the United States, aquamarines can be found at the summitof Mt. Antero in the Sawatch Range in central Colorado. In Brazil, there are mines in the states of Minas Gerais, Espírito Santo and Bahia.The biggest aquamarine ever mined was found at the city of Marambaia, Minas Gerais. It weighed over 110 kg, and its dimensions were 48.5 cm long and 42 cm in diameter.Aquamarine is the birthstone associated with March.

Cameo
Cameo is a method of carving, or an item of jewelry made in this manner. The effect of "cameo" also refers to a proof coin that has frosted lettering and features, providing attractive contrast with the mirrored fields of the coin. The terms "deep cameo" and "ultra cameo" describe cameo coins having the boldest, most attractive contrast.A cameo is usually made of two types of material, commonly precious or semi-precious stone. One material is carved into a figure — the most common type being a profile portrait of a person's head. This is then set upon the other type of material which provides a background of another color to set off the figure. Cameos are often worn as jewelry. Cameos of great artistry were made in Greece dating back as far as the 6th century BC. Cameos were very popular in Ancient Rome and have enjoyed periodic revivals, notably in the early Renaissance, and again in the 17th and 18th centuries.

Citrine
Citrine, also called citrine quartz or citrine topaz, is an amber-coloured gemstone. It is a form of quartz with ferric iron impurities, and is rarely found naturally. Most commercial citrine is in fact artificially heated amethyst or smoky quartz. Brazil is the leading producer of naturally mined citrine, with much of its production coming from the state of Rio Grande do Sul.In ancient times, citrine was carried as a protection against snake venom and evil thoughts.Citrine is one of two traditional birthstones for the month of November.

Coral
Corals are gastrovascular marine cnidarians (phylum Cnidaria; class Anthozoa) existing as small sea anemone-like polyps, typically forming colonies of many individuals. The group includes the important reef builders known as hermatypic corals, found in tropical oceans, and belonging to the subclass Zoantharia of order Scleractinia (formerly Madreporaria). The latter are also known as stony corals in as much as the living tissue thinly covers a skeleton composed of calcium carbonate. A coral "head" is formed of many individual polyps, each polyp only a few millimetres in diameter. The colony of polyps functions essentially as a single organism by sharing nutrients via a well developed gastrovascular network, and the polyps are clones, each having the same genetic structure. Each polyp generation grows on the skeletal remains of previous generations, forming a structure that has a shape characteristic of the species, but subject to environmental influences.The hermatypic corals obtain much of their nutrient requirement from symbiotic unicellular algae called zooxanthellae, and so are dependent upon growing in sunlight. As a result, these corals are usually found not far beneath the surface, although in clear waters corals can grow at depths of 60 m (200 ft). Corals breed by spawning, with many corals of the same species in a region releasing gametes simultaneously over a period of one to several nights around a full moon.Corals are major contributors to the physical structure of coral reefs that develop only in tropical and subtropical waters. Isolated corals exist even in cold waters, such as off the coast of Norway. The most extensive development of extant coral reef is the Great Barrier Reef off the coast of Queensland, Australia. Indonesia is home to 581 of the world's 793 known coral reef-building coral species.

Crystal
A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions.Generally, fluid substances form crystals when they undergo a process of solidification. Under ideal conditions, the result may be a single crystal, where all of the atoms in the solid fit into the same lattice or crystal structure but, generally, many crystals form simultaneously during solidification, leading to a polycrystalline solid. For example, most metals encountered in everyday life are polycrystals. Crystals are often symmetrically intergrown to form crystal twins.Which crystal structure the fluid will form depends on the chemistry of the fluid, the conditions under which it is being solidified, and also on the ambient pressure. The process of forming a crystalline structure is often referred to as crystallization.

Cubic Zirconia
Cubic Zirconia (or CZ) is zirconium oxide (ZrO2), a mineral that is extremely rare in nature but is widely synthesized for use as a diamond simulant. The synthesized material is hard, optically flawless and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate (ZrSiO4).Because of its low cost, durability, and close visual likeness to diamond, synthetic cubic zirconia has remained the most gemologically and economically important diamond simulant since 1976. Its main competition as a synthetic gemstone is the more recently cultivated material moissanite.

Diamonds
Diamond is one of the two best known forms (or allotropes) of carbon, whose hardness and high dispersion of light makes it useful for industrial applications and jewelery. The other equally well known allotrope is graphite;but diamonds are specifically renowned as a mineral with superlative physical qualities. They make excellent abrasives because they can only be scratched by other diamonds, which also means they hold a polish extremely well and retain luster. About 130 million carats (26,000 kg) are mined annually, with a total value of nearly 9 billion dollars.The name "diamond" derives from the ancient Greek adamas (αδάμας; "impossible to tame"). They have been treasured as gems since their use as religious icons in India at least 2,500 years ago—and usage in drill bits and engraving tools also dates to early human history. Popularity of diamonds has risen since the 19th century because of improved cutting and polishing techniques, and they are commonly judged by the "four Cs": carat, clarity, color, and cut. Nearly four times the mass of natural diamonds are produced as synthetic diamond each year, though these are typically classified with poor-quality specimens that are suitable only for industrial-grade use.Most natural diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, Russia, Brazil, and Australia. They are generally mined from volcanic pipes, which are deep in the Earth where the high pressure and temperature enables the formation of the crystals. The mining and distribution of natural diamonds are subjects of frequent controversy—such as with concerns over the sale of conflict diamonds by African paramilitary groups. There are also allegations that the De Beers Group misuses its dominance in the industry to control supply and manipulate price via monopolistic practices.

Emeralds
Emerald (Be3Al2SiO6) is a variety of the mineral beryl, colored green by trace amounts of chromium and sometimes iron. It is highly prized as a gemstone and by weight is the most valuable gemstone in the world, often made more so by inclusions. Beryl has a hardness of 8 on the 10 point Mohs scale of hardness.Emerald is a rare and valuable gemstone and, as such, provided the incentive for developing synthetic emeralds. Both hydrothermal and flux-growth synthetics have been produced and a method has been developed for producing an emerald overgrowth on colorless beryl. Synthetic emeralds fluoresce a dull red with long wave UV light due to an indicator added during the process of synthesizing the emerald, whereas natural specimens do not. Also both the specific gravities (natural: 2.70 - 2.78, synthetic: 2.66) and refractive indices (natural: 1.576 - 1.582, synthetic: 1.565) of synthetics are slightly lower. Wispy inclusions are common in flux-grown synthetic emeralds.

Enamel
In a discussion of art technology, enamel (or vitreous enamel, or porcelain enamel in American English) is the colorful result of fusion of powdered glass to a substrate through the process of firing, usually between 750 and 850 degrees Celsius. The powder melts and flows to harden as a smooth, durable vitreous coating on metal, glass or ceramic. It is often applied in a paste form and may be transparent or opaque when fired. Vitreous enamel can be applied to most metals.Also, an "enamel" is a decorative object, usually very small, having an enamel coating, such as a piece of champlevé or cloisonné.Vitreous enamel has many excellent properties: it is smooth, hard, chemically resistant, durable, can take on long-lasting, brilliant colors, and cannot burn. Disadvantages are its tendency to crack or shatter when the substrate is stressed or bent.The durability of enamel has given it many functional applications, including: early 20th century advertising signs, interior walls of ovens, speckleware cooking pots, exterior walls of high quality kitchen appliances, cast iron bathtubs, storage silos on farms and process equipment such as chemical reactors and tanks for the chemical and pharmaceutical process industries.Enamelling is an old and widely-adopted technology. The ancient Egyptians applied enamels to pottery and stone objects. Other practitioners include the ancient Greeks, Celts, Russians, and the Chinese.The bright, jewel-like colors have also made enamel a favored choice for designers of jewelry and bibelots, such as ancient beads, the fantastic eggs of Peter Carl Fabergé , enameled copper boxes of Battersea enamellers, and artists such as George Stubbs and other painters of portrait miniatures. Enameling was a favorite technique of the Art Nouveau jewellers.

Garnets
The Garnet group of minerals show crystals with a habit of rhombic dodecahedrons and trapezohedrons. They are nesosilicates with the same general formula, A3B2(SiO4)3. The chemical elements in garnet include calcium, magnesium, aluminium, iron2+, iron3+, chromium, manganese, and titanium. Garnets show no cleavage and a dodecahedral parting. Fracture is conchoidal to uneven; some varieties are very tough and are valuable for abrasive purposes. Hardness is 6.5 - 7.5, specific gravity is 3.1 - 4.3, luster is vitreous to resinous, and they can be transparent to opaque.The name "garnet" comes from the Latin granatus, a grain possibly in reference to malum garanatum (pomegranate) a plant with red seeds similar in shape, size and color to some garnet crystals.There is a misconception that garnets are only a red gem but in fact they come in a variety of colors including purple, red, orange, yellow, green, brown, black, or colorless. The lack of a blue garnet was remedied in 1990's following the discovery of color-change blue to red/pink material in Bekily, Madagascar but these stones are very rare. Color-change garnets are by far the rarest garnets except uvarovite, which does not come in cuttable sizes. In daylight, their color can be shades of green, beige, brown, gray and rarely blue, to a reddish or purplish/pink color in incandescent light. By composition, these garnets are a mix of spessartine and pyrope, as are Malaya garnets. The color change of these new garnets is often more intense and more dramatic than the color change of top quality Alexandrite which is frequently disappointing, but still sells for many thousands of dollars (US) per carat. It is expected that blue color-change garnets will match Alexandrite prices or even exceed them as the color change is often better and these garnets are much rarer. The blue color-change type is mainly caused by relatively high amounts of vanadium (about 1 wt.% V2O3).Six common varieties of garnet are recognized based on their chemical composition. They are pyrope, almandine or carbuncle, spessartite, grossularite (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and andradite. The garnets make up two solid solution series; 1. pyrope - almandine -spessarite and 2. uvarovite-grossularite-andradite.Garnet is the birthstone for January, and has been used since the Bronze Age.

Moissanite
Moissanite is a trade name given to silicon carbide (chemical formula SiC) for use in the gem business. As a gemstone, silicon carbide is similar to diamond in several important ways: it is transparent and extremely hard (9 1/4 on the Mohs scale, compared to 10 for diamond), with an index of refraction between 2.65 and 2.69 (compared to 2.42 for diamond). SiC has a hexagonal crystalline structure.Naturally occurring moissanite is extremely rare, as it is not formed naturally in any quantity within the Earth, and thus is found only in tiny quantities in certain types of meteorite and as microscopic traces in corundum deposits and kimberlite. Virtually all of the silicon carbide sold in the world, including moissanite gemstones, is synthetic. Natural moissanite was first found in 1905 as a small component of a meteorite in Arizona by Dr. Ferdinand Henri Moissan, after whom the material is named in the gem market. Synthetic silicon carbide has been known since 1892, when it was first produced by Eugene G. Acheson in his newly invented resistance furnace. Acheson named the material carborundum by analogy to corundum, another very hard substance (9 on the Mohs scale). Moissan's discovery of naturally occurring SiC was disputed at first due to the potential for contamination of his sample by silicon carbide saw blades that were already on the market at that time.In 1998 C3, Inc. (Charles and Colvard), a subsidiary of Cree Research, Inc., introduced gem-quality synthetic silicon carbide onto the market under the name "moissanite," marketing it as a lower-cost alternative to diamond. Touted as the best, most convincing diamond simulant to date, moissanite kicked up quite a stir: Journalists and programmes such as Nova reported on the troubling ease of misidentification between moissanite and diamond, citing incidents of fraud.While some properties of moissanite are closer to diamond than those of cubic zirconia, another synthetic diamond simulant, once its properties are known, moissanite is perhaps even easier to identify. Jewellers were at first fooled by moissanite's thermal conductivity which approximates that of diamond, rendering older thermal testers useless; what worked with cubic zirconia did not work with moissanite.Moissanite is much harder than cubic zirconia (9 1/4 vs. 8 1/2), lighter (SG 3.33 vs. 5.6), and much more resistant to heat. This results in a stone of higher lustre, sharper facets and extraordinary resilience: loose moissanites may be placed directly into ring moulds, the stones surviving unscathed from temperatures up to twice the 900°C melting point of 18k gold.

Onyx
Onyx is a banded variety of chalcedony, a cryptocrystalline form of quartz. The colours of its bands are white and black. It is usually cut as a cabochon, or into beads, and is also used for intaglios and cameos. Some onyx is natural but much is produced by the staining of agate.

Opals
The mineraloid opal is amorphous SiO2·nH2O; hydrated silicon dioxide, the water content sometimes being as high as 20%. Opal ranges from colorless through white, milky blue, gray, red, yellow, green, brown and black. Often many of these colors can be seen at once, caused by interference and diffraction of light passing through minute, regularly arranged apertures within the microstructure of opal, known as Bragg's lattice. These apertures are filled with secondary silica and form thin lamellae inside the opal during solidification. The term opalescence is commonly and erroneously used to describe this unique and beautiful phenomenon, which is correctly termed play of color. Contrarily, opalescence is correctly applied to the milky, turbid appearance of common or potch opal. Potch does not show a play of color.The veins of opal displaying the play of color are often quite thin, and this has given rise to unusual methods of preparing the stone as a gem. An opal doublet is a thin layer of colorful material, backed by a black mineral, such as ironstone, basalt or obsidian. The darker backing emphasizes the play of color, and results in a more attractive display than a lighter potch. Given the texture of opals, they can be quite difficult to polish to a reasonable lustre. The triplet cut backs the colored material with a dark backing, and then has a cap of clear quartz (rock crystal) on top, which takes a high polish, and acts as a protective layer for the comparatively delicate opal.

Pearls
A pearl is a hard, rounded object produced by certain mollusks, primarily oysters. Pearl is valued as a gemstone and is cultivated or harvested for jewellery.Pearls are formed inside the shell of certain bivalve mollusks. As a response to an irritating object inside its shell, the mollusk will deposit layers of calcium carbonate (CaCO3) in the form of the minerals aragonite or calcite (both crystalline forms of calcium carbonate) held together by an organic horn-like compound called conchiolin. This combination of calcium carbonate and conchiolin is called nacre, or as most know it, mother-of-pearl.The unique luster of pearls depends upon the reflection and refraction of light from the translucent layers and is finer in proportion as the layers become thinner and more numerous. The iridescence that some pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface. Pearls are usually white, sometimes with a creamy or pinkish tinge, but may be tinted with yellow, green, blue, brown, or black. Black pearls were highly valued because of their rarity; however, this does not apply nowadays as black pearl production has significanly increased.

Peridot
Peridot (pronounced pear-e-doe) is the gem quality variety of forsterite olivine. It is bright yellow-green in color, and has a hardness of 6.5 on Mohs scale. The chemical composition of peridot is (Mg, Fe)2SiO4. Peridot is one of the few gemstones that come in only one color. The depth of green depends on how much iron is contained in the crystal structure, and varies from yellow-green to olive to brownish green. Peridot is also often referred to as "poor man's emerald". Olivine is a very abundant mineral, but gem quality peridot is rather rare. Peridot crystals have been collected from iron-nickel meteorites.Peridot is found in Arizona, Hawaii, Nevada, and New Mexico, in the US, and in Australia, Brazil, China, Kenya, Mexico, Myanmar (Burma), Norway, Pakistan, South Africa, Sri Lanka, and Tanzania. The largest cut peridot is a 310 carat (62 g) specimen in the Smithsonian Museum in Washington, D.C.. A special variety of peridot from Pakistan is known as "Cashmere" peridot. Due to the large size of the rough stones found there, cutters have successfully created faceted stones of over 100 carats (20 g) from the rough gems of this area.It is the birthstone for the month of August. According to folklore, the peridot will bring its wearer success, peace, and good luck. Peridot has been found in Egyptian jewellery from the early second millennium BCE and was mined from the volcanic island of Zebirget, or St. Johns Island, in the Red Sea. Native Hawaiians referred to peridot crystals as the tears of Pele, the Goddess-of-Fire.

Rhinestones
A rhinestone is an imitation diamond made from rock crystal, glass or acrylic. Originally, rhinestones were rock crystals gathered from the river Rhine, but their availability was greatly increased when the French jeweller George Frederic Strass had the idea to coat the lower side of glass with metal powder around 1775, imitating diamonds. Hence, rhinestones are called Strass in the German language.In 1955, the Aurora Borealis, a coating applied to crystal stonesto produce a rainbow of colors effect was introduced. Today, crystal rhinestones are primarily used on costumes, apparel and jewelry. They are produced mainly in Austria and the Czech Republic, while acrylic rhinestones are manufactured in several countries.Heavy use of rhinestones is often associated with country music singers, as well as with Elvis Presley and Liberace. The rhinestone-studded Nudie suit was invented by Nudie Cohn in the 1940s, an Americanization of the matador's "suit of lights".

Rubies
Ruby is a red gemstone, a variety of the mineral corundum (aluminium oxide) in which the color is caused mainly by chromium. Its name originates from ruber, Latin for red. Natural rubies are exceptionally rare, though artificial ones (sometimes called created ruby) can be manufactured which are comparatively inexpensive.Rubies are mined in Africa, Asia, Australia and Greenland. They are most often found in Myanmar, Sri Lanka and Thailand, though they have also been found in Montana and South Carolina. Sometimes spinels are found along with rubies in the same geological formations and are mistaken for the more valuable gem. However, fine red spinels may approach the average ruby in value.Rubies have a hardness of 9 on the Mohs scale of mineral hardness, and among the natural gems are only surpassed by diamonds in hardness. Other varieties of corundum are called sapphires.Ruby gemstones are valued according to several characteristics including size, color, clarity and cut. All natural rubies have imperfections in them. On the other hand, artificial rubies may have no imperfections. The fewer the number and the less obvious the imperfections, the more valuable the ruby is—unless there are no imperfections (i.e., a "perfect" ruby), in which case it is suspected of being artificially made and its status as a priceless gem is therefore not assured. Some manufactured rubies have dopants added to them so that they can be identified as artificial, but most require gemological testing to determine their origin.A synthetic ruby crystal was used to create the first laser.Ruby is the birthstone associated with July.

Sapphires
Sapphire is any gemstone-quality corundum. (The red variety of corundum is also known as ruby.)When color is not specified, sapphire refers to the blue variety. Pink, yellow, green, white, and parti-color (multi-colored) sapphires are often valued less than the blue variety of the same quality and size. However a pink-orange sapphire, called a padparadsha, is highly prized. They were found in many countries especially in Asia such as India, Sri Lanka, Thailand, Myanmar, and Cambodia.It is the impurities in the aluminium oxide crystal that give the color variations, with different impurity chemical elements giving the different colors that can be found. Pure sapphire is transparent. Traces of iron and titanium give sapphires a blue color. The crystals are exceptionally hard, with only diamond being harder among natural gems. They have a hardness of 9 on the Mohs hardness scale (Diamond is 10).Gem quality sapphires and rubies occur naturally and can be easily and cheaply produced in the laboratory. The chemical compositions and physical properties are identical to the natural sapphires. The tell-tale sign of synthetic sapphires is the crystalline growth lines which are usually curved due to the pulling during the accelerated crystal growth process.A version which shows an asterism is called a star sapphire (see picture above). Although natural sapphires can show an asterism, the shape of the star is usually somewhat irregular and sometimes indistinct. A manufactured star sapphire called the Linde Star shows a very regularly-shaped and distinct asterism because the formation process is more tightly controlled than the natural version.The Logan sapphire is one of the largest blue sapphire gems known. It weighs 423 carats (84.6 g).Lady Diana Spencer's engagement ring from Charles, Prince of Wales was a sapphire ring.Cornflower blue is one of the most popular colors for sapphires (the other choice color a deep royal blue), though there is little objective consensus about which shade of blue is the most cornflower or the most desirable.Sapphire is also the birthstone associated with September.

Silver
Silver is a chemical element in the periodic table that has the symbol Ag (from the traditional abbreviation for the Latin Argentum, from which the Argentina is named) and atomic number 47. A soft white lustrous transition metal, silver has the highest electrical and thermal conductivity of any metal and occurs in minerals and in free form. This metal is used in coins, jewelry, tableware, and photography.Silver is a very ductile and malleable (slightly harder than gold) univalent coinage metal with a brilliant white metallic luster that can take a high degree of polish. It has the highest electrical conductivity of all metals, even higher than copper, but its greater cost has prevented it from being widely used in place of copper for electrical purposes.Pure silver also has the highest thermal conductivity, whitest colour, the highest optical reflectivity (although it is a poor reflector of ultraviolet), and the lowest contact resistance of any metal. Silver halides are photosensitive and are remarkable for the effect of light upon them. This metal is stable in pure air and water, but does tarnish when it is exposed to ozone, hydrogen sulfide, or air with sulfur in it. The most common oxidation state of silver is +1; a few +2 compounds are known as well.

Topaz
The mineral topaz is a silicate of aluminium and fluorine with the chemical formula (AlF)2SiO4. It is orthorhombic and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. It has an easy and perfect basal cleavage and so gemstones or other fine specimens should be handled with care to avoid developing cleavage flaws. The fracture is conchoidal to uneven. Topaz has a hardness of 8, a specific gravity of 3.4-3.6, and a vitreous lustre. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. They may also be white, gray, green, blue, or reddish-yellow and transparent or translucent. When heated, yellow topaz often becomes reddish-pink. It can also be irradiated, turning the stone a light and distinctive shade of blue. A recent trend in jewelry is the manufacture of topaz specimens that display iridescent colors, by applying a thin layer of titanium oxide via physical vapor deposition.Topaz is found associated with the more acid rocks of the granite and rhyolite type and may be found with fluorite and cassiterite. It can be found in the Ural and Ilmen mountains, Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico, and the United States.The name "topaz" is derived from the Greek topazos, "to seek," which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be a yellowish olivine) was mined in ancient times. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above.Topaz is also the birthstone of November.

White Gold
White gold refers to an alloy of gold and other white metals such as silver, palladium, or nickel. The natural color of white gold is light gray, so jewelry made of white gold is typically coated in highly reflective rhodium (sometimes coated in platinum and palladium), adding a more brilliant shine. Palladium and silver alloys are of higher quality than nickel and are sometimes not coated with rhodium. The purpose of plating is to add luster to grayer jewelry, as well as to prevent oxidation of some of the metals found in the alloys. White gold is not platinum, but is used as a cheaper alternative, usually costing one-third as much as platinum.At the turn of the 20th century, a relatively unknown metal called platinum was being combined with diamonds by some jewelers. However, platinum was very expensive. White gold alloys were developed in the 1920s as a less expensive alternative to platinum. To meet the growing demand, several different alloys based on gold-nickel-palladium, in different combinations, became commercially available. During World War II, the use of platinum and nickel for nonwar-related applications was prohibited. As a result, palladium-based white gold alloys became the only choice for consumers in the U.S. In addition to higher costs, white gold jewelry based on palladium alloys are denser and heavier than nickel-based alloys. They are also not as white in color. After the war, lower-cost nickel-based white gold quickly once again became the dominant choice of the jewelry industry worldwide

Yellow Gold
Gold is a chemical element in the periodic table that has the symbol Au (L. aurum) and atomic number 79. A soft, shiny, yellow, dense, malleable, ductile (trivalent and univalent) transition metal, gold does not react with most chemicals but is attacked by chlorine, fluorine and aqua regia. The metal occurs as nuggets or grains in rocks and in alluvial deposits and is one of the coinage metals.Gold is used as a monetary standard for the International Monetary Fund (IMF). For millenia, it has been used as money by many nations and is also used in jewelry, dentistry, and in electronics. Its ISO currency code is XAU.Gold is a metallic element with a characteristic yellow color, but can also be black or ruby when finely divided, while colloidal solutions are intensely colored and often purple. These colors are the result of gold's plasmon frequency lying in the visible range, which causes red and yellow light to be reflected, and blue light to be absorbed. It is one of only three metals which have an actual easily-identifiable color; the other two are copper, which is red, and caesium, which has a pale golden color.