A
gold nugget is a naturally occurring piece of
native gold.
Watercourses often concentrate nuggets and finer gold in
placers. Nuggets are recovered by
placer mining, but they are also found in residual deposits where the gold-bearing
veins or
lodes are weathered. Nuggets are also found in the
tailings piles of previous mining operations, especially those left by
gold mining dredges. 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 2007 study of Australian nuggets ruled out speculative theories of
supergene formation via
in-situ precipitation,
cold welding of smaller particles, or bacterial concentration, since the crystal structures of all nuggets examined proved they were originally formed at high temperature deep underground (i.e., they were of
hypogene origin). Nuggets are usually 20.5 to 22
karat (k) purity, meaning they are 83% to 92% gold by
mass. Gold nuggets in
Australia are often 23 k or slightly higher, while
Alaskan nuggets are usually at the lower end of the spectrum. Purity can be roughly assessed by nugget color: the richer and deeper the orange-yellow, the higher the gold content. Nuggets are also referred to by their
fineness, for example "865 fine" means the nugget is 865
parts per thousand in gold by mass. The common impurities are
silver and
copper. Nuggets high in silver content constitute the alloy
electrum. Two gold nuggets are claimed as the largest in the world: the
Welcome Stranger and the Canaã nugget, the latter being the largest surviving natural nugget. Considered by most authorities to be the biggest gold nugget ever found, the Welcome Stranger was found at
Moliagul, Victoria, Australia in 1869 by John Deason and Richard Oates. It had a
gross weight of over and returned over net. The Welcome Stranger is sometimes confused with the similarly named
Welcome Nugget, which was found in June 1858 at Bakery Hill, Ballarat, Australia by the Red Hill Mining Company. The Welcome Nugget weighed . It was melted down in London in November 1859. Large nuggets are still being found around the world. On 16 January 2013, a large gold nugget was found near the city of
Ballarat in Victoria, Australia by an amateur gold prospector. The Y-shaped nugget weighed slightly more than , measured around 22 cm high by 15 cm wide, and has a market value slightly below 300,000
Australian dollars, though opinions have been expressed that it could be sold for much more due to its rarity. The discovery has cast doubt on the common rumour that
Victoria's goldfields were exhausted in the 19th century. == List of nuggets ==