Types of Gold

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Gold can be found in rock veins and gravels, and in clay and silt deposited by rivers and streams. The main types of gold you may come across are:

• Lode gold or Reef gold - formed in rock veins either on or below the surface.
• Alluvial gold or Placer gold - gold that has been carried far from its original source - carried by rivers, streams and floods. Alluvial gold or placer gold exists in the form of gold nuggets, fine gold particles and ranges in color from yellow to black, in its original combination with other metals.
• Gold Bullion - precious metal in gold bar or gold ingot form. This term is also applied to consignments of coins.
• Gold alloy - when pure gold ("chuk kam" in Chinese) is utilised for jewelry it is rarely used in its pure state (24k). Gold is usually alloyed with other metals to give the gold different attributes. When wearing gold it is hardly ever actual gold, it is gold alloy. And in legal terms, any "gold" item less that 12K (50%, .500, 500 fineness) cannot be called gold, because it is more than 50% something else.
• Rolled gold - this is formed by fusing a block of gold on top of a larger block of base metal. The fused blocks are then rolled out repeatedly until a sheet of the required width is achieved.
• Gold plate - produced by either dipping, electroplating or spraying gold metal onto a base metal.
• Colloidal Gold - is a suspension of nanometric-sized particles of gold in a fluid, usually water.
• Isotopic Gold - gold has one stable isotope, ¹⁹⁷Au, and 18 radioisotopes.
• Gold Leaf - pure gold (24k) hammered to a fine sheet. Gold leaf is used in electroscopes and for decoration.
• Fool's gold - iron pyrites, which is a gold-colored iron ore. Once valueless, it is now used in the large scale production of sulphuric acid. It is thought to be the "gold" that Sir Francis Drake brought back from the New World on his first trip, and subsequently bankrupted a number of prominent Elizabethans who financed a second trip to get more. No gold was ever extracted from the ore retrieved.

Lode gold is also known a reef gold. Lode gold occurs in veins, grains or microscopic particles of metallic gold embedded in rock. Ores bearing native gold consist of gold nodules, often in association with veins of quartz or pyrites.

These are called "lode" deposits.

Owing to oxidation of related minerals, followed by weathering, free gold is richer at the surface of gold-bearing veins. Gold occurs mainly in pyrite- and polymetallic sulphide–quartz vein / veinlets.

A gold lode deposit can be found at the surface or can be found deep underground by following the gold vein. Lode gold yields a higher percentage of gold to incorporation material than placer gold, so the grade of gold deposit in terms of grams / tonne (g/t) would normally be higher. This can be outweighed by the cost of extraction.

Native gold is found as free flakes, grains or larger nuggets that have been eroded from rocks by water and other erosion mechanisms and deposited as alluvial or placer deposits.

Alluvial describes soil that has been deposited by flowing water. It can be of clay, silt, sand, gravel or other substance. Alluvial Gold is gold dust deposited along with alluvial soil. Water causes the washing of gold dust into streams and rivers, where it collects. Over time this can result in the gold flakes being welded, by the water action, to form gold nuggets.

Alluvial gold can be panned from riverbed soil by scooping up the alluvial material and washing through with water. The heavy gold sinks to the bottom and is left as a residual for collection.

Placer gold is that gold weathered from the original host rock. Placer gold has then been deposited or "placed" elsewhere, for example on a hillside (eluvial placer), stream or lake bed .

Bullion gold bars are the traditional method for purchasing gold. Good London Delivery (GLD) gold bars are 12.5 kg (400 oz), 24 karat, 999.5% or better fineness. This is the form of gold bullion that central banks hold, as they are a convenient size and weight.

However, there are more convenient weights for investment purposes:

• 1 kilogram (32.15 oz)
• 10oz
• 1oz
• 10g
• 100g
• 1 Tael
• 1 Tola

Some countries allow these to be bought or sold at their major banks

• Argentina
• Austria
• Liechtenstein
• Switzerland

Elsewhere there are bullion dealers. Bullion dealers provide the same service as the major banks. Bullion bars carry a lower price premium than gold bullion coins.

Large bullion bars can be forged, so gold buyers often have bullion bars re-assayed, especially if they are dated older than 5 years. Bullion coins, on the other hand, can be weighed and measured against known parameters.

Initiatives by manufacturers such as Argor Heraeus (ch), with Kinebars™ having holographic technology are gradually combating gold bar counterfeiting. For every initiative however, there are many determined people who are devising new methods to counterfeit and seeking ways to scam potential gold buyers.

Pure gold (24k) is soft and very malleable.

The carat gold alloys range in gold content from 8 to 22 carats (8k to 22k).

Metallurgists must take into consideration how various precious metals react to one another. Formulating gold alloys is very challenging. Too much of one precious metal can cause the combination to become fragile, hard and will prove difficult to design jewelry and other decorative items. Another combination of precious metal may cause the alloy to become too soft for jewelry fabrication.

All gold alloys have different mechanical properties such as strength, hardness and malleability (ductility) and some alloys can be heat treated to maximise strength and hardness.

There are hundreds of gold alloys and gold mixtures possible. Generally the addition of silver will color gold green. The addition of copper will color it red. A mix of about 50wt%:50wt% copper : silver will give a range of yellow gold alloys: those that you are accustomed to seeing at the jewelry store.

There are some more unusual alloys of gold. Where gold is mixed with silver, iron, cadmium or aluminium one can obtain green, blue and purple gold compounds. Another technique, which involves the formation of a colored oxide layer on the alloy during heat treatment in air, is surface oxidation.

The term "rolled gold" is often used interchangeably with "gold fill". "Gold fill" probably gives you a better idea of what rolled gold is.

"Rolled gold" describes the manufacturing process where gold (14k or other grade) is layered on top of a base metal and then rolled until you are left with an outer cylinder of gold around a core of base metal.

"Gold fill" is a better term for those that wish to visualize the end product. Although the fill is really just the core of the product, it can be visualized as being the electric copper wire within an electric flex. The copper wire is never seen and the surrounding flex is durable and ensures the copper does not come into contact with anything. Such is rolled gold.

In jewelry terms the gold is what comes into contact with your skin. It is effectively just like 'the real thing'. Everything you can do with gold, you can do with rolled gold. The only difference being .....the cost.

There is 100 times more gold in rolled gold than in gold plate.

Rolled gold is not exactly like gold fill but it serves it's roll for explanation purposes..

Colloidal gold is also known as nanogold. Colloidal gold is a suspension of nanometric-sized particles of gold in a fluid, usually water. The liquid is typically either an intense red color or a dirty yellowish color, according to the size of particles.

Michael Faraday (late 1850's) began the evaluation of colloidal gold's unique electronic, optical and molecular-recognition properties. Gold nanoparticles are the subject of substantial research. Colloidal gold has applications in electronics, nanotechnology, electron microscopy and materials science.

Ruby red glass is colored by colloidal suspensions of gold nanoparticles. The same effect is used for purple-red to pink decorative glass enamel for tableware and glass. Colloidal gold, known as ‘Purple of Cassius’, is an ancient technology.

Colloidal silver is yellow and alloys of colloidal gold and silver are used in decorative glass enamels to shift the purple color towards pink.

In the current exciting world of nanotechnology research, nanoshells are an interesting development. They consist of a metal such as gold coated onto a dielectric core such as silica. These absorb light and so have a characteristic color that depends on the relative metal thickness:core size.

The color is produced by a plasmon resonance mechanism. When the gold shells are made thinner, the purple color shifts to greens and blues.

Gold (Au, Aurum) has one stable isotope, ¹⁹⁷Au, and 18 radioisotopes.

¹⁹⁵Au is the most stable with a half-life of 186 days.

¹⁹⁸Au is used for treating cancer. implanted in tissues it serves as a radiation source in the treatment of certain cancers.

Radioactive gold is used in diagnosis. It is injected in a colloidal solution and tracked as a beta emitter whilst passing through the body.

Gold plate is either a dip of gold metal, electroplate or is sprayed on. It does not last as long as rolled gold.

Gold plating deposits a thin layer of gold onto the surface of copper, silver or other metal, thus making silver-gilt for example, by an electrochemical or chemical process.

Originally, gold plate (and silver plate) meant (before about 1800 AD) a high grade of precious metal used for making ecclesiastical and prestigious precious metal wares. It now means a baser product that only has a coating of the precious metal over a base metal core.

Gold has the highest malleability of any metal. This essential property lends itself to gold leaf creation. Gold leaf is an ultra-thin layer of pure gold. It is created using metal rollers capable of compressing gold to a thickness of only 1/250,000^th of an inch. Gold is an element, so it can be compressed, theoretically, to one atom thickness without destroying its structure.  Gold leaf is extremely fragile and adheres to most moistened surfaces. It is prepared for use by cutting it into small sheets and sandwiching it between layers of glassine paper. Glassine paper is one to which gold leaf will not adhere..

The thin gold sheets are used for gilding. Gold leaf is available in a wide variety of karats and shades. 24 Karats is pure gold. 22-karat yellow gold is the most common. Real yellow gold leaf is about 92% (.92 fineness). Silver colored white gold is around 50% (.5 fineness).

Water gilding is highly regarded, and difficult, form of gold leafing. Gold leafing has been practised by hand by skilled artisans for hundreds of years. The skill of gold leafing has remained virtually unchanged throughout that time.