Gold

Gold is a chemical element with the symbol Au (from its Latin name aurum) and atomic number 79. It is a highly sought-after precious metal, having been used as money, as a store of value, in jewelry, in sculpture, and for ornamentation since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, underground "veins" and in alluvial deposits. Gold is dense, soft, shiny and the most malleable and ductile substance known. Pure gold has a bright yellow color traditionally considered attractive. It is one of the coinage metals and formed the basis for the gold standard used before the collapse of the Bretton Woods system in 1971. The ISO currency code of gold bullion is XAU.

Modern industrial uses include dentistry and electronics, where gold has traditionally found use because of its good resistance to oxidative corrosion. Chemically, gold is a transition metal and can form trivalent and univalent cations upon solvation. At STP it is attacked by aqua regia, forming chloroauric acid and by alkaline solutions of cyanide but not by hydrochloric, nitric or sulphuric acids. Gold dissolves in mercury, forming amalgam alloys, but does not react with it. Gold is insoluble in nitric acid, which will dissolve silver and base metals, and is the basis of the gold refining technique known as "inquartation and parting". Nitric acid has long been used to confirm the presence of gold in items, and this is the origin of the colloquial term "acid test," referring to a gold standard test for genuine value.


Gold is the most malleable and ductile of all metals; a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become translucent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red.

Gold readily creates alloys with many other metals. These alloys can be produced to increase the hardness or to create exotic colors (see below). Gold is a good conductor of heat and electricity, and is not affected by air and most reagents. Heat, moisture, oxygen, and most corrosive agents have very little chemical effect on gold, making it well-suited for use in coins and jewelry; conversely, halogens will chemically alter gold, and aqua regia dissolves it via formation of the chloraurate ion.

Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated out as gold metal by adding any other metal as the reducing agent. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.

Doctoral research undertaken by Frank Reith at the Australian National University, and publised in 2004, shows that microbes can play an important role in forming gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits.

High quality pure metallic gold is tasteless; in keeping with its resistance to corrosion (it is metal ions which confer taste to metals).

In addition, gold is very dense, a cubic meter weighing 19300 kg. By comparison, the density of lead is 11340 kg/m³, and that of the densest element, osmium, is 22610 kg/m³.

Color of gold

Mainly, Gold appears to be metallic yellow. Gold, caesium and copper are the only elemental metals with a natural color other than gray or white. The usual gray color of metals depends on their "electron sea" that is capable of absorbing and re-emitting photons over a wide range of frequencies. Gold reacts differently, depending on subtle relativistic effects that affect the orbitals around gold atoms.

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Diamond Ring

In Western tradition, an engagement ring is a ring worn by a woman indicating her engagement to be married. In some countries, such as the United Kingdom, it is worn on the left-hand ring finger, while in other countries, such as Poland and Ukraine, it is customary for the ring to be worn on the right-hand. By modern convention in countries such as the United States, the ring is usually presented as a betrothal gift by a man to his prospective bride while or directly after she accepts his marriage proposal. It represents a formal agreement to future marriage.

Similar traditions purportedly date to classical times, dating back from an early usage reportedly referring to the fourth finger of the left hand as containing the vena amoris or "vein of love".

In the United States and Canada today it is becoming more common, but still quite rare, that a woman will also buy an engagement or promise ring for her partner at the time of the engagement.

In Egypt, Brazil and many European countries, both the man and the woman usually wear engagement rings, most often in the form of matching plain bands of white, yellow, or rose gold.[citation needed] In these countries the man's engagement ring often also eventually serves as the wedding ring. Some men wear two rings, but this is rarer. The woman's wedding ring can sometimes have a precious stone. In Spain, the woman sometimes buys a wristwatch for the man as an engagement present.

In some countries the tradition has been for the future groom to privately select and purchase a ring, to be presented to his desired bride when he proposes.
An 18k gold banded engagement-wedding-anniversary ring combination.

With more and more couples living together prior to marriage, however, it is becoming more common for a couple to select the engagement ring while purchasing a wedding band together. In countries where both partners wear engagement rings, the matching rings tend to be purchased together. In the United States the ring is to be worn on the left ring finger (4th finger) for both men and women.

The price for an engagement ring can vary considerably depending on the materials used, the value of the gemstone, and the retailer. A conventional buying price ranging from two to three months wages for a ring guideline originated from De Beers marketing materials in the early 20th century, in an effort to increase the sale of diamonds.

When shopping for a diamond ring, the price can depend significantly on the carat weight, color, clarity and cut of the diamond, otherwise known as gemological characteristics of the diamond. While less frequent, the practice of using other gemstones such as sapphires, rubies, moissanite, emeralds, occurs to honor tradition, reduce the price of the ring, or to make it unique.

Refusing the gift

Women traditionally refuse offers of marriage by refusing to take the offered engagement ring. In some states of the United States, engagement rings are considered "conditional gifts" under the legal rules of property. This is an exception to the general rule that gifts cannot be revoked once properly given. See, whose ruling found the following reasoning persuasive: "the so-called 'modern trend' holds that because an engagement ring is an inherently conditional gift, once the engagement has been broken, the ring should be returned to the donor. Thus, the question of who broke the engagement and why, or who was 'at fault,' is irrelevant. This is the no-fault line of cases."

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Diamond

In mineralogy, diamond (from the ancient Greek ἀδάμας, adámas) is the allotrope of carbon where the carbon atoms are arranged in an isometric-hexoctahedral crystal lattice. Its hardness and high dispersion of light make it useful for industrial applications and jewelry. It is the hardest known naturally-occurring mineral. It is possible to treat regular diamonds under a combination of high pressure and high temperature to produce diamonds (known as Type-II diamonds) that are harder than the diamonds used in hardness gauges. Presently, only aggregated diamond nanorods, a material created using ultrahard fullerite (C60) is confirmed to be harder, although other substances such as cubic boron nitride, rhenium diboride and ultrahard fullerite itself are comparable.

Diamonds are specifically renowned as a material with superlative physical qualities; they make excellent abrasives because they can be scratched only by other diamonds, borazon, ultrahard fullerite, rhenium diboride, or aggregated diamond nanorods, which also means they hold a polish extremely well and retain their lustre. Approximately 130 million carats (26,000 kg (57,000 lb)) are mined annually, with a total value of nearly USD $9 billion, and about 100,000 kg (220,000 lb) are synthesized annually.

They have been treasured as gemstones since their use as religious icons in ancient India and usage in engraving tools also dates to early human history. Popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns. They are commonly judged by the “four Cs”: carat, clarity, color, and cut.

Roughly 49% of diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil, and Australia. They are mined from kimberlite and lamproite volcanic pipes, which can bring diamond crystals, originating from deep within the Earth where high pressures and temperatures enable them to form, to the surface. The mining and distribution of natural diamonds are subjects of frequent controversy such as with concerns over the sale of conflict diamonds (aka blood diamonds) by African paramilitary groups.

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Pearl

A pearl is a hard, roundish object produced within the soft tissue (specifically the mantle) of a living shelled mollusk. Just like the shell of mollusks, a pearl is composed of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes of pearls (baroque pearls) occur.

The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries, and because of this, the word pearl became a metaphor for something very rare, very fine, very admirable and very valuable.

Almost any shelled mollusk can, by natural processes, produce some kind of "pearl" when an irritating microscopic object becomes trapped within the mollusk's mantle folds, but virtually none of these "pearls" are valued as gemstones. Although malacologists may refer to these objects as "pearls", gemologists classify them merely as calcareous concretions.
A black pearl and a shell of the black-lipped pearl oyster
A black pearl and a shell of the black-lipped pearl oyster
Saltwater pearl oyster farm, Seram, Indonesia
Saltwater pearl oyster farm, Seram, Indonesia

Nacreous pearls, the most desirable pearls, are produced by two groups of molluscan bivalves or clams. One family lives in the sea: the pearl oysters. The other, very different group of bivalves live in freshwater, and these are the river mussels; for example, see the freshwater pearl mussel.

Saltwater pearls can grow in several species of marine pearl oysters in the family Pteriidae. Freshwater pearls grow within certain (but by no means all) species of freshwater mussels in the order Unionida, the families Unionidae and Margaritiferidae. These various species of bivalves are able to make nacreous pearls because they have a thick iridescent inner shell layer called "mother of pearl", which is composed of nacre. The mantle tissue of a living bivalve can create a pearl in the same manner that it creates the pearly inner layer of the shell.

Fine gem-quality saltwater and freshwater pearls can and do sometimes occur completely naturally in the wild state, but this is rare. Many hundreds of pearl oysters or pearl mussels have to be gathered and opened, and thus killed, in order to find even one wild pearl, and for many centuries that was the only way pearls were obtained. This was the main reason why pearls fetched such extraordinary prices in the past. In modern times however, almost all the pearls for sale were formed with a good deal of expert intervention from human pearl farmers.
A pearl being extracted from an akoya pearl oyster
A pearl being extracted from an akoya pearl oyster

A nacreous pearl is made from layers of nacre, by the same living process as is used in the secretion of the mother of pearl which lines the shell. A "natural pearl" is one that formed without any human intervention at all, in the wild, and is very rare. A "cultured pearl", on the other hand, is one that has been formed on a pearl farm. The great majority of pearls on the market are cultured pearls.

Imitation or fake pearls are also widely sold in inexpensive jewelry, but the quality of the iridescence is usually very poor, and generally speaking, fake pearls are usually quite easy to distinguish from the real thing.

Pearls have been harvested, or more recently cultivated, primarily for use in jewelry, but in the past they were also stitched onto lavish clothing, as worn, for example, by royalty. Pearls have also been crushed and used in cosmetics, medicines, or in paint formulations.

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