Tuesday, December 16, 2008

Gold

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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.

Monday, December 15, 2008

Diamond Ring

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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."