Natural gold nuggets are never 100% pure gold. That is the short answer. Natural alloys of various metals naturally occur with gold in its natural form. The refining process is needed to remove these impurities to produce gold bullion that is truly pure.
Matrix in the Nuggets
It is worth noting that we are not talking about impurities that are found as a matrix on some gold nuggets. This might include quartz, ironstone, or iron staining down in the grooves of the nugget. Yes, these are also impurities, but they are not a part of the metal itself, rather they are attached to the outside of the gold nugget.
While this stuff is certainly not gold, understand that even when a nugget is thoroughly cleaned of its matrix, the gold metal itself still has natural impurities.
Natural Alloys in Natural Gold Nuggets
No matter where gold is mined on Earth you will find various alloys in the gold, most commonly silver and copper. Silver is most common, and in some areas it is not common for a gold nugget to have as much as 20% or more silver content. When this occurs it is technically called electrum, although most folks still call it gold.
Electrum is a natural occurrence that is very common in some goldfields. It is pretty easy to identify a piece of electrum when it is found. Rather than having a rich gold color like you would expect from the average gold nugget, electrum is often very dull, silvery or brassy colored. Sometimes it even shows a slight greenish tint to it.
There have been quite a few beginner prospectors who have tossed electrum aside when they found it, not realizing what it was. In the United States, one area where electrum is commonly found in in the state of Nevada, but it has been found in many other mining districts also.
Even nuggets that are bright, shiny and have a rich golden color still have a small amount of impurities in them, and they are never 100% pure.
The silver and copper alloys found in natural nuggets can also alter their color by giving them a slightly darker patina. This patina can be desirable for collectors who prefer to keep their gold nuggets in their natural condition. Polishing a nugget can often change its color, giving it not only a shinier appearance, but a somewhat lighter shade as well.
The purity of gold nuggets varies from state-to-state. In fact, each mining district will generally produce different purities of gold. Variations in purity can even be seen in the same location, where it is apparent that different gold veins have eroded and the gold dust and nuggets that have broken off from the main vein show different colors and textures.
Where does the Purest Gold Come From?
As we just mentioned, the natural variations in gold purity can be seen even at the same location, so making a statement that gold from a certain area will always be of a certain purity may not be accurate.
Just making a generalized statement like “gold from California is more pure than gold from Oregon” or “Alaskan gold has more impurities than other gold” is not really true or accurate. These statements are much too general. While this may be true some of the time, there is no guarantee of that. Gold can vary a lot from different locations.
I have seen Alaskan gold ranging from around 70% pure and up to as high as 92% pure. The same can be said for many other states.
Australia is a country that is well-known for having gold that is naturally high purity. Many areas produce nuggets that are 95% purity and higher. If you want to buy a nugget that is high purity, then Australian gold nuggets are often a good choice, but they aren’t the only place. I have seen gold from several states in the West and a few even in the Southeast that also produce very high purity gold to would rival the nicest nuggets from Australia.
There are acid test kits and various other devices that you can use to test the purity of a gold nugget. However, let me tell you right now that none of these devices are completely accurate. Even the fancy tools used by many of the major refineries to offer quotes on precious metals are not all that accurate.
The ONLY way to truly determine the purity of a gold nugget would be to melt it down and refine the metal. Only by removing the impurities and determining the actual gold weight can you be certain of its purity, but doing this would remove the intrinsic value of a natural gold nugget. Therefore, refining might be a good choice for more common placer gold dust, but is not recommended for larger gold nuggets.
Does the Purity of a Nugget even Matter?
IN MY OPINION, the purity of a natural gold nugget only affects its value to the extent that it is visually attractive to the gold or mineral collector. Obviously, a gold nugget that has a high gold content that is bright and shiny will be of more value to a collector than one that is lower purity and dull colored.
Remember that the color of a gold nugget is not the only thing that you use to value it though. The overall shape and texture has a lot to do with the value. Crystalline gold is often valued much higher than a smooth gold nugget even if it has a naturally high silver content.
Subtle differences in purity simply do not have much of an effect on a gold nuggets value in my experience. If the nugget is of significant size and of interest to a collector, whether it is 85% purity of 90% purity really doesn’t matter. A collectible gold nugget is already worth more than the “melt value” of the gold anyway.