Gold is also the most malleable and ductile substance known. It can be flattened out to less than. Gold is also one of the most resistant metals. It won't tarnish , discolor, crumble, or be affected by most solvent s. This adds on to the uniqueness and allure of this mineral.
Gold is usually associated with Pyrite and other sulfides , and sometimes may not be noticed because of the association with these resembling minerals. In certain localities, minerals that contain these sulfides are heated high enough for the sulfides to dissolve, enabling the Gold to remain intact on the matrix. Such Gold is known as "Roasted Gold", and is occasionally sold to collectors.
For additional information, see the gemstone section on Gold. Picture Rock. Let us know how we can update this page Click for more details. We strive for accurate content and locality information.
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If you are requesting a locality be added, please only include significant locality occurences for the mineral. About Minerals. Link Directory Donations Mobile Site. Chemical Formula. Gold, with small amounts of silver; sometimes also copper and iron. Variable Formula.
Golden yellow to brass yellow. Golden yellow. Crystal System. Crystal Forms and Aggregates. Octahedral , dodecahedral , and cubic crystals occur, as well as combinations of these forms, but they are uncommon and are often distorted. Dendrite s, wires , nugget s, encrustation s, and small flakes are the more common forms.
Crystals are often stacked into elongated groups, and may form in lines or patterns, especially in herringbone formation. Spinel twin ning in groups of small crystals is well-known habit. Crystals may form in hopper growths. Specific Gravity. Ductile and malleable. Other ID Marks. Later, weathering released the gold nuggets that end up in a stream due to gravity. Nuggets are gold fragments weathered out of an original lode. They often show signs of abrasive polishing by stream action, and sometimes still contain inclusions of quartz or other lode matrix material.
A study on Australian nuggets ruled out speculative theories of supergene formation via in-situ precipitation, cold welding of smaller particles, or bacterial concentration, since crystal structures of all of the nuggets examined proved they were originally formed at high temperature deep underground i.
Other precious metals such as platinum form nuggets in the same way. A later study of native gold from Arizona, US, based on lead isotopes indicates that a significant part of the mass in alluvial gold nuggets in this area formed within the placer environment.
Nuggets are usually Gold nuggets in Australia 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. Most nuggets are between 85 percent and 95 percent pure gold, but the remainder can be one of several kinds of minerals. Nuggets in laterite can be either reddish or black; nuggets in quartz appear cloaked with white.
A specimen gold nugget is a matrix of gold and other rock, usually quartz or ironstone in Australia. If the gold to rock ratio is high, and the shape shows off a lot of the gold at the surface, your nugget can hold a higher value. It found in residual deposits where the gold-bearing veins or lodes are weathered. The best areas for finding gold nuggets are those which are known for producing coarse gold. Scanning with a metal detector is the most common, practical method for finding gold nuggets and other forms of gold.
Coarse gold did not occur in all gold fields, even when some were considered especially rich. In some areas of Australia the gold is fine and concentrated in crevices in bedrock and any gravel wash overlying this. Even fairy tales often mention golden objects such as eggs or harps, and most people have heard of the golden pot at the end of the rainbow. Gold had a significant historical role in Australia.
However, early discoveries of gold in Australia were hushed up by the authorities for fear that all the convicts, soldiers and public servants would stop work to hunt for their fortune. In , the Rev. When he showed the gold to Governor Gipps, the Governor said, "Put it away, Mr Clarke or we shall all have our throats cut!
It wasn't until ten years later, in , that Edward Hargraves who had just returned from the gold fields in California and his colleagues found gold near Bathurst. This time the find was publicised and within a month a thousand men were looking for gold. The area was called Ophir, after the biblical story about King Solomon's gold city. The Bathurst gold rush was followed by discoveries in Victoria.
Gold fever drew tens of thousands of immigrants from many parts of the world to the Australian colonies. Ballarat and Bendigo in Victoria became major gold sites. In , gold miners on the Ballarat diggings were angry at the unfair miner's licence system. They fought against troopers in the famous Eureka Stockade battle, the only armed rebellion in Australia's history.
In the early s, great finds were made at Coolgardie and Kalgoorlie in Western Australia. Within 10 years of the gold rushes to Bathurst, Ballarat and Bendigo, Australia's population trebled to more than one million people.
Gold discoveries spurred the development of inland towns, communications, transport and foreign trade. Although gold boosted Australia's development, its importance declined during most of the 20th century as other minerals became of greater economic significance.
It underwent a resurgence in the s and s when the application of new technology allowed lower grade ores to be processed economically. Gold has changed where and how people live. Many towns have been developed by the wealth from mining gold and Australia also has many 'ghost towns' - when the gold supply ran out, people simply deserted the area. The term 'digger', the nickname for Australian soldiers fighting overseas, comes from the fact that many of the World War I soldiers had literally been diggers in the goldfields just before the war.
The most common natural method of concentration of gold is through the ancient action of hot fluid inside the Earth's crust. Fluids deep in the crust are heated by the Earth's internal heat. These fluids often have moved through the rocks over a large area and 'dissolved' the gold. When these fluids cooled or reacted with other rocks the dissolved gold precipitated came out of the fluid in cracks or fractures forming veins.
If the fluids move over a large enough area, and dissolve the gold for a long enough period of time, gold can be concentrated in amounts in the parts per thousand or even greater. In Australia this concentration of gold took place in the Earth hundreds of millions of years ago in the eastern states, and thousands of millions of years ago in Western Australia.
As well as gold, the fluids can carry other dissolved minerals, such as quartz. This is why gold is often found with quartz.
These are known as primary gold deposits and to extract the gold the rock containing the veins of gold has to be dug up mined , crushed and processed. Some rocks containing gold veins have been exposed on the surface and are eroding away.
The gold that these rocks contained has been washed down into creeks to form alluvial placer gold deposits. Here, the gold is further concentrated by the action of water. Because gold is heavier than most of the material moved by a creek or river, it can become concentrated in hollows and trapped in the bed of the river. These are known as secondary alluvial gold deposits and they can be worked using a gold pan or cradle.
Alluvial gold deposits sparked the Australian gold rushes of the 's. Mostly, gold is spread throughout the rocks and soil around us but in such low amounts that it's not worthwhile trying to get it out.
However, there are some places where there is enough gold to make it economic to mine. Most gold mined in Australia today cannot be seen in the rock, it is very fine grained and mostly has a concentration of less than 5 grams in every tonne of rock mined.
The feasibility of mining low concentrations of gold largely depends on the price of gold. Gold is bought and sold every day on international gold markets. The price fluctuates according to demand by buyers and the amount being sold by sellers. In a few places gold is sufficiently concentrated in the rocks for it to be worth mining.
Australia especially Western Australia is the one of the world's top producers of gold. Virtually all resources occur in primary deposits, many of which have undergone some degree of weathering. Weathered primary deposits are important to the gold industry because they are usually easier and cheaper to mine and the gold is easier to recover. At Olympic Dam SA gold occurs and is mined with copper and uranium. Secondary deposits are no longer major sources of gold in Australia. Gold usually occurs in its metallic state, commonly associated with sulphide minerals such as pyrite, but it does not form a separate sulphide mineral itself.
The only economically important occurrence of gold in chemical combination is with tellurium as telluride minerals. Replica of the Welcome Nugget. The largest gold nugget ever found was the 'Welcome Stranger', found in just under the soil at the base of a tree!
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