Pyrite vs gold: how to tell them apart
In 1577 Martin Frobisher sailed back to England from Baffin Island with around 200 tons of ore he was certain contained gold. Queen Elizabeth I had invested. The following year he went back and returned with over a thousand tons more. Furnaces were built at Dartford specifically to process it. After five years of trying, everyone accepted what several assayers had said at the start: it was iron pyrite, worth nothing. Some of it reportedly ended up as road stone.
If a Tudor expedition with royal backing and professional assayers could get this wrong at that scale, nobody should feel foolish about a promising-looking pebble from a stream. The good news is that the tests which settle it are simple, they use things already in your house, and you can run most of them without damaging anything.
Here they are, roughly in order of how much they cost you.
First, know what you're probably holding
The US Geological Survey names three minerals that commonly get called fool's gold, and it's worth knowing which one you have.
Pyrite is iron sulfide, FeS₂, and the classic culprit. Pale brassy yellow, hard, brittle, and often forming sharp cubes.
Chalcopyrite is copper iron sulfide, and it's arguably the better impostor: it's a deeper, more convincing golden colour than pyrite. It's softer at Mohs 3.5 to 4, and it frequently tarnishes to iridescent purples and blues, which is a giveaway once you've seen it.
Biotite mica catches more people than either, and surprises everyone. It's a dark mineral that weathers into thin, flexible, brassy flakes. A flash of sunlight off a mica flake in a pan looks exactly like fine gold to a tired eye at the end of a long day.
One more, occasionally: pyrrhotite, another iron sulfide, brassy and metallic. It's easy to eliminate because it's magnetic, which none of the others are.
The free test: watch how it behaves in light
Before touching anything, tilt it and change the lighting. This costs nothing and it resolves a surprising number of cases.
Gold glows. It has a soft, even, buttery yellow shine that looks the same from every angle, and crucially, it looks the same in shade as it does in sunlight.
Pyrite and mica sparkle. Their flat crystal faces act as tiny mirrors, so they flash brightly at one angle and go dull at another. Move them into shade and they turn a duller brassy yellow or darken noticeably.
The old prospector's version of this is the sun and shade test, and it's genuinely reliable: carry the pan into the shade. Pyrite and mica stop performing. Gold carries on looking like gold.
If it flashes at you, it's probably not gold. Gold just sits there being golden.
The test that actually settles it: streak
Rub the specimen firmly across a piece of unglazed porcelain. The back of a bathroom tile works, or the unglazed foot ring on the underside of a mug.
Gold leaves a golden-yellow streak, the same colour as the metal.
Pyrite leaves a greenish-black to brownish-black streak. Chalcopyrite leaves greenish-black too.
This is the test to reach for, because a mineral's streak, its colour in powdered form, is far more consistent than its surface colour. It's also the point at which most "is this gold" questions end.
Two practical notes. Gold is soft enough that it tends to smear rather than powder, which is itself informative. And if your specimen is a tiny flake in a pan, streak testing isn't practical, so skip to the squash test below.
Hardness, and why the copper coin trick fails in Britain
Gold is soft, at Mohs 2.5 to 3. Pyrite is hard, at 6 to 6.5. That's a wide gap and it should be easy to exploit.
Every guide online tells you to scratch the specimen with a copper coin. In Britain, that advice is out of date, and it will give you a wrong answer.
UK 1p and 2p coins were bronze, roughly 97% copper, until September 1992. Since then they've been copper-plated steel, and the copper plating is about 0.025mm thick. Scratch a mineral with a post-1992 penny and you're not testing with copper at all; you're scraping through a fraction of a millimetre of plating onto a steel core, and steel is around Mohs 4 to 4.5. A material that should have resisted a copper coin may get marked anyway.
There's an easy check. Hold a magnet to the coin. Pre-1992 bronze coins are not magnetic. Post-1992 copper-plated steel coins are. If your penny jumps to the magnet, it's not a copper test.
Use a steel knife or nail instead, which is more useful anyway because the gap is wider. Steel sits around Mohs 5.5. If the blade marks your specimen easily, that's consistent with gold. If the specimen scratches the blade and leaves a silvery smear behind, it's pyrite.
The squash test
This is the most conclusive of the physical tests, and the one that destroys pyrite, so keep it for material you don't mind damaging.
Put the specimen on something hard and press or tap it firmly with a hammer, or push a pin into a small flake.
Gold is malleable and ductile. It flattens, dents, spreads. It behaves like soft metal, because that's what it is.
Pyrite is brittle. It shatters, cracks, or crumbles to dark powder.
For a tiny flake in a pan, a pin is enough. Gold squashes flat. Pyrite disintegrates.
Wear eye protection if you're using a hammer, and don't run this test on a nice pyrite crystal or anything you'd want to keep.
Weight
Gold is extraordinarily dense. Pure gold has a specific gravity of 19.3, meaning it weighs 19.3 times the same volume of water. Pyrite sits at 4.9 to 5.2.
That's roughly a fourfold difference, and it's obvious in the hand: a gold nugget feels absurdly heavy for its size.
One correction worth knowing, because most articles state 19.3 as though it's what you'd find in a stream. Natural gold is usually alloyed with silver, sometimes enough to be called electrum, which brings the density of real nuggets down to roughly 15 to 18. Still enormously heavier than anything else in the pan, but if you're calculating a specific gravity at home and getting 16 rather than 19.3, that's normal for natural gold rather than evidence against it.
This is also why panning works at all. Gold drops straight to the bottom. Mica floats around near the top and washes out. Pyrite tends to sit somewhere in between.
Shape
Pyrite forms sharp cubes, twelve-sided pyritohedra, and octahedra, often with fine parallel striations across the faces. Those flat mirror faces and hard geometric edges are unmistakable once you've seen them.
Gold does form crystals, but they're rare and usually crude. What you actually find is irregular: rounded nuggets, flakes, wires, dendritic sprays, spongy masses. Placer nuggets get their rounded shape from tumbling in water.
So a perfect little brassy cube is pyrite. Gold essentially never presents itself that neatly.
If it turns out to be pyrite
Frobisher's ore was worthless to him because he wanted gold. Pyrite itself is far from worthless.
Its name comes from the Greek pyr, meaning fire, because it throws sparks when struck against steel. It was used as a fire starter long before it was ever mistaken for treasure, and later in the flintlock's predecessor, the wheellock. Industrially, pyrite is a major source of sulfur dioxide for producing sulfuric acid, which is one of the most heavily used industrial chemicals in the world.
It's also, as an object, genuinely beautiful, and it's one of the very few minerals that grows in near-perfect cubes without any human involvement. That's worth something on its own.
One practical note for anyone keeping it. Pyrite slowly oxidises in the presence of oxygen and moisture, producing sulfuric acid, faster if the specimen is powdery or has a high surface area. It's a storage consideration rather than a safety scare, and we've covered where pyrite sits among the genuinely hazardous minerals separately.
The bottom line
Six tests, in the order you should use them. Tilt it in changing light and take it into shade. Rub it on unglazed porcelain and look at the streak. Try to scratch it with a steel blade. Squash a small piece if you can spare it. Feel the weight. Look at the shape.
The streak test alone settles most cases. Streak plus squash settles essentially all of them.
And if you're in Britain, don't use a penny minted after September 1992 as your copper standard, because it isn't copper in any meaningful sense.
The pattern underneath all of this is the one that runs through everything we do here. Surface appearance is the least reliable property a mineral has, which is exactly why the trade can sell dyed howlite as turquoise and glass as cherry quartz. Colour lies. Streak, hardness, density and habit don't. Every specimen we list carries its species, its documented origin and its treatment status, so you never have to work it out from a photograph. Know what you own.
Sources: The three common gold look-alikes per the U.S. Geological Survey. Pyrite, chalcopyrite, pyrrhotite and gold physical properties, including streak, hardness, specific gravity and habit, per Geology.com, Minerals.net and standard mineralogical references. Native gold density range in natural nuggets per New Mexico Bureau of Geology and corroborating sources on gold-silver alloying. Frobisher voyage tonnages and the identification of the ore as iron pyrite per Royal Museums Greenwich and Encyclopaedia Britannica. UK 1p and 2p coin composition, the September 1992 change to copper-plated steel, and the resulting magnetism per The Royal Mint; plating thickness of 0.025mm per Compound Interest. Pyrite etymology and its use in sulfuric acid production per USGS and standard references.