Natural gold nuggets are rare, and that makes them a target for look-alikes. The good news is that real gold behaves in ways that are hard to fake. Here are the checks collectors use, from quick at-home tests to professional testing, and what to look for when you buy.
1. Look at the color and surface
Natural gold has a warm, buttery yellow color that looks the same from every angle and never tarnishes. Pyrite ("fool's gold") and chalcopyrite look brassy or greenish, glitter with sharp flat faces, and often dull or rust over time. A real nugget usually shows rounded, water-worn edges from tumbling in a stream, and may hold bits of quartz, ironstone or clay in its crevices.
Be careful with pieces that look too perfect. Melted and cast "nuggets" often have a uniform, bubbly or grainy texture and the same look all over, while natural nuggets vary from one spot to the next.
2. Check how it handles pressure
Gold is soft and malleable. Pressed with a pin it dents instead of chipping. Pyrite and other look-alike minerals are brittle and will crack or flake. Only try this on rough, low-value pieces, never on a nugget you plan to sell or display.
3. Do a streak test
Rub a small corner across the back of an unglazed ceramic tile. Real gold leaves a golden-yellow streak. Pyrite leaves a greenish-black streak and chalcopyrite a dark green-black one. Like the pressure test, this leaves a small mark, so use it on lower-value material.
4. Try a magnet
Gold is not magnetic. If a "nugget" jumps to a strong magnet, it is not gold or it has an iron core. A nugget that ignores the magnet still isn't proven real, because many fakes use non-magnetic metals, but it is a fast way to rule things out.
5. Check the weight and density
Gold is very heavy for its size. Pure gold has a density of about 19.3 grams per cubic centimeter, and natural nuggets, which contain some silver, usually fall somewhere around 15 to 19. A specific gravity test compares a nugget's weight in air with its weight in water to estimate its density. A piece that feels light for its size is a red flag. Quartz and ironstone inside a nugget will lower the reading, so specimens need extra care.
6. Get it professionally tested
The most reliable answer comes from professional testing such as X-ray fluorescence (XRF), which reads metal content without harming the nugget. Avoid acid tests on a nugget you care about, because acid can stain or damage the surface.
How we handle it at Sierra Gold Exchange
Every lot of gold we sell is tested, and every sealed slab is tested and labeled with the nugget's weight, purity, origin and a unique serial number. You can look up any slab serial number on our Verify Your Gold page. Every nugget is one of a kind, and you receive the exact piece shown in the photos.
Browse our natural gold nuggets and gold specimens, or email info@sierragoldexchange.com with any questions.