Gold nugget - AbsoluteAstronomy.com

"Gold nugget" may also refer to the catfish Baryancistrus xanthellus
Baryancistrus xanthellus
Baryancistrus xanthellus is a species of Loricaria in the Ancistrini tribus.It is a benthic fresh water fish that lives i Rio Xingu in the Amazon system...

or the mango cultivar Gold Nugget
Gold nugget
A gold nugget is a naturally occurring piece of native gold. Watercourses often concentrate and grow the nuggets. Nuggets are recovered by placer mining, but they are also found in residual deposits where the gold-bearing veins or lodes are weathered...

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A gold nugget is a naturally occurring piece of native gold. Watercourse

Watercourse

A watercourse is any flowing body of water. These include rivers, streams, anabranches, and so forth.-See also:* physical geography* Environmental flow* Waterway* Hydrology* Wadi-External links:...

s often concentrate and grow the nuggets. Nuggets are recovered by placer mining

Placer mining

Placer mining is the mining of alluvial deposits for minerals. This may be done by open-pit or by various surface excavating equipment or tunneling equipment....

, but they are also found in residual deposits where the gold-bearing veins

Vein (geology)

In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation...

or lode

Lode

In geology, a lode is a deposit of metalliferous ore that fills or is embedded in a fissure in a rock formation or a vein of ore that is deposited or embedded between layers of rock....

s are weathered. Nuggets are also found in the tailings

Tailings

Tailings, also called mine dumps, slimes, tails, leach residue, or slickens, are the materials left over after the process of separating the valuable fraction from the uneconomic fraction of an ore...

piles of previous mining operations, especially those left by gold mining

Gold mining

Gold mining is the removal of gold from the ground. There are several techniques and processes by which gold may be extracted from the earth.-History:...

dredges.

Formation

Many nuggets are formed by cold welding

Cold welding

Cold or contact welding is a solid-state welding process in which joining takes place without fusion/heating at the interface of the two parts to be welded. Unlike in the fusion-welding processes, no liquid or molten phase is present in the joint....

of smaller particles and fragments in streams and rivers. Gold's softness makes it prone to welding under impact or hammering loads, such as those produced at waterfalls and in rapids. There is no oxide surface layer to inhibit adhesion between gold flakes. So when pieces of gold hit one another under pressure, they may join into a bigger piece. Some nuggets may have been present in massive form in the original vein before erosion, often showing signs of abrasive polishing by stream action. (Other precious metals such as platinum

Platinum

Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...

form nuggets in the same way.) The exceptional ductility

Ductility

In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized...

and malleability of gold means brittle fracture is rare.

Composition

Nuggets are usually 20K to 22K purity (83% to 92%). Gold nuggets in Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

often are 23K or slightly higher, while Alaskan nuggets are usually at the lower end of the spectrum. Purity can be roughly assessed by the nugget color, the richer and deeper the orange-yellow the higher the gold content. Nuggets are also referred to by their fineness

Fineness

The fineness of a precious metal refers to the ratio of the primary metal to any additives or impurities.A piece of alloy metal containing a precious metal may have the weight of its precious component referred to as its fine weight. For example, 1 troy ounce of 18 karat gold may be said to have a...

, for example "865 fine" means the nugget is 865 parts per thousand in gold. The common impurities are silver

Silver

Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

and copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

. Nuggets high in silver content constitute the alloy electrum

Electrum

Electrum is a naturally occurring alloy of gold and silver, with trace amounts of copper and other metals. It has also been produced artificially. The ancient Greeks called it 'gold' or 'white gold', as opposed to 'refined gold'. Its color ranges from pale to bright yellow, depending on the...

Largest specimens

The largest gold nugget found was the Welcome Stranger

Welcome Stranger

The "Welcome Stranger" is the name given to the largest alluvial gold nugget ever found, which had a calculated refined weight of 2,283 oz 6 dwts 9 gr...

, found at Moliagul, Victoria

Moliagul, Victoria

Moliagul is a small township in Victoria, Australia, 202 kilometres north west of Melbourne, notable for the discovery of the world's largest gold nugget, the Welcome Stranger in 1869...

, Australia in 1869 by John Deason and Richard Oates. It weighed gross, over 2520 troy ounces (78.4 kg) and returned over 2284 troy ounces (71 kg) net. It eclipsed the Welcome Nugget

Welcome Nugget

The Welcome Nugget was the name given to a large gold nugget, weighing 2,217 troy ounces 16 pennyweight. , that was discovered by a group of twenty-two Cornish miners at the Red Hill Mining Company site at Bakery Hill in Ballarat, Victoria, on June 9, 1858...

found eleven years earlier in Ballarat.

The largest gold nugget found using a metal detector

Metal detector

A metal detector is a device which responds to metal that may not be readily apparent.The simplest form of a metal detector consists of an oscillator producing an alternating current that passes through a coil producing an alternating magnetic field...

is the Hand of Faith

Hand of Faith

The Hand of Faith is a nugget of fine-quality gold that was found by Kevin Hillier using a metal detector near Kingower, Victoria, Australia on 26 September 1980. Weighing 875 troy ounces , the gold nugget was only 12 inches below the surface, resting in a vertical position...

, weighing 875 troy ounce

Troy ounce

The troy ounce is a unit of imperial measure. In the present day it is most commonly used to gauge the weight of precious metals. One troy ounce is nowadays defined as exactly 0.0311034768 kg = 31.1034768 g. There are approximately 32.1507466 troy oz in 1 kg...

s, found in Kingower, Victoria

Kingower, Victoria

Kingower is a small town in Victoria, Australia, located on Inglewood-Rheola Road, in the Shire of Loddon. The town was once very populated during the times of the Victorian Gold Rush.- History :...

, Australia in 1980.