Gold nuggets are naturally occurring large masses of native gold found in alluvial deposits. Often they are concentrated by watercourses and recovered by placer mining. In other instances, gold nuggets are found in piles of residue in sites where mining operations once took place.
Two gold nuggets are noted for being the largest masses of gold ever discovered. These are the "Welcome Stranger" and the "Hand of Faith". Their respective "largest" titles, however, carry further qualifications.
The Welcome Stranger Gold Nugget:
The exact distinction given of this gold nugget is: "the largest alluvial gold nugget ever found". It was discovered on February 5, 1869 at Moliagul, a small township in Victoria, Australia about 37 miles west of the city of Bendigo. The discoverers, John Deason and Richard Oates, found the nugget just a couple inches below the surface on a slope in a place that's sometimes called Black Reef.
Records have the following details about the Welcome Stranger:
• Gross weight: 3,523.5 troy ounces (241.61 pounds)
• Trimmed weight: 2,520 troy ounces (172.8 pounds)
• Net weight: 2,315.5 troy ounces (158.78 pounds)
• Measurement: 2 feet (0.61 meter) x 1.02 feet (0.31 meter)
For their find, Deason and Oates were paid about £19,068 by the London Chartered Bank (located in the town of Dunolly in Victoria), where they took the nugget.
The Welcome Stranger no longer exists today, although the gold from it understandably still does. Also, there exist two replicas of the nugget. One is in possession of the descendants of John Deason, while the other is in the City Museum in Treasury Place, in Melbourne.
The Hand of Faith Gold Nugget:
This gold nugget actually carries two distinctions: "the largest gold nugget found by a metal detector" and "the largest gold nugget currently in existence". It was discovered on September 26, 1980 somewhere near the small town of Kingower in Victoria, Australia.
The nugget's discoverer, Kevin Hillier, was aided by a metal detector in this precious find. Hillier found the nugget in a vertical position just a foot below the surface.
The Hand of Faith weighs 874.82 troy ounces (60 pounds) and measures 1.54 feet (0.47 meter) x 0.66 feet (0.20 meter) x 0.30 feet (0.09 meter). The Golden Nugget Casino in Las Vegas, Nevada currently houses the nugget. Its sale price was reportedly around 1 million U.S. dollars.
Gold nuggets actually are not composed of pure 24K gold. A safer estimate would be that they're somewhere between 20K and 23K. Those found in Australia often have higher purity than the ones found in Alaska. The color of a nugget often provides a clue as to the purity of its gold content. Nuggets that have very rich deep orange/yellow color are sure to have higher gold content than pale ones.
Also, there is a system called "millesimal fineness" which is used to denote the purity of gold alloy (also of silver and platinum alloys) by parts per thousand of pure metal by mass in the alloy. A nugget containing 91.6% gold, for example, is denoted as "916 fine". This fineness is equivalent to 22K.
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Items of jewelry or art made of precious metals are hallmarked based on specific requirements either of the country of import or the place of manufacture. Such items, particularly those made of silver, gold, or platinum, are struck with an official mark (or series of marks), which guarantees fineness or purity of the metal used.
To determine the precious metal content in an item, certain non-destructive assay techniques are used. Two examples are the touchstone method (a very old assay method) and the X-ray fluorescence method (the modern, non-destructive assay method). While these assay methods are suited for finished goods (again because they are non-destructive), three other methods are more suited for raw precious metals:
Titration:
This assay method is one of the most widely used laboratory technique, which involves the analysis and determination of unknown concentration of a given reactant. It is used to assay silver bullion or stock. In this method, a reagent (titrant) of a known volume and concentration is utilized to react with a solution of the substance being analyzed (titrand), whose concentration is unknown.
With the use of an instrument called burette (to add the titrant), the exact consumed amount, on reaching the endpoint, can be determined. The endpoint refers to the point at which the assay is complete. The completion is signaled by an indicator. There are at least four types of titration. These are acid-base, redox, complexometric, and Zeta potential.
Cupellation:
This technique is considered the most exact, elaborate, and destructive method of assay and is best suited for gold bullion or stock. Also called fire assay, the method involves treating ores or alloyed metals under high temperatures and carefully controlled operations to separate gold from base metals (copper, zinc, or lead), which may be present in the ore. Once the base metals are heated at high temperatures, the gold (as well as the other precious metals that may be present) remains apart and the other non-precious metals react forming other compounds. Cupellation basically has two processes: large scale and small scale.
Spectrometry:
This method is best used to assay platinum bullion or stock. With the use of a spectrometer or spectrograph, the amount or concentration of a given substance is assessed. The substances are identified through the spectrum they absorb or emit. This assay method has several types. These include absorption, fluorescence, X-ray, flame, visible, ultraviolet, infrared, photoemission, Mossbauer, nuclear magnetic resonance, and Raman.
Again, the X-ray fluorescence (XRF) method is the modern assay method widely used today for analyzing precious metals, including (besides silver, gold, and platinum) rhenium, ruthenium, iridium, and palladium. As a non-destructive assay method, XRF can identify various elements in a substance (in fact, even in powder and liquid ones) within a few minutes.
One of the most important aspects in any of the assay methods pertains to the accurate determination of the composition of a substance at various points in the process. Controlling and minimizing metal losses can only be achieved through close monitoring of the composition of the work in progress.
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