Fool's gold. Brittle where gold is malleable, streaks greenish-black where gold streaks yellow, and a quarter of gold's density.
Spain, Peru, Italy, and almost every sulphide deposit on earth6 field tests
More people arrive at a mineral identification wanting to know whether they have found gold than for any other reason, and the overwhelming majority are holding pyrite. It is not a close call once you know what to do — pyrite and gold differ on almost every physical property there is — but they are genuinely similar in colour and metallic lustre, which is all a photograph shows.
The decisive difference is behaviour under a pin. Gold is a soft, malleable metal: press or scratch it and it dents and smears, and a sliver cut from it bends. Pyrite is a hard, brittle sulphide: press it and it crumbles into angular grit, and it will scratch a copper coin where gold will not.
The second decisive difference is weight, and it is not subtle. Gold's specific gravity is 19.3. Pyrite's is about 5.0. A gold nugget feels absurd in the hand — like picking up a stone that has been switched for lead — and pyrite simply does not.
This is the comparison that answers the question people actually came with, so it is set out in full. Every row can be checked without equipment beyond a porcelain tile, a copper coin and a pin.
The streak test is the one to run if you can only run one. Rub the specimen firmly across an unglazed tile — the back of a bathroom tile works, or the base of a ceramic mug. Gold leaves a yellow metallic smear. Pyrite leaves a greenish-black to brownish-black powder, which is the colour of the mineral pulverised rather than the colour of its surface.
| Property | Pyrite | Gold |
|---|---|---|
| Mohs hardness | 6 – 6.5 — scratches glass and a copper coin | 2.5 – 3 — a copper coin scratches it |
| Streak on unglazed tile | Greenish-black to brownish-black | Yellow, metallic |
| Specific gravity | About 5.0 | 19.3 — startlingly heavy |
| Behaviour under a pin | Brittle: crumbles to angular grit | Malleable: dents and smears |
| Crystal habit | Cubes, pyritohedrons, striated faces | Irregular nuggets, dendrites, wires |
| Colour in shadow | Pale brassy, sometimes greenish | Deep buttery yellow, unchanged |
| Tarnish over years | Dulls, may develop rust and sulphur smell | Never tarnishes |
| Sparks with steel | Yes — the origin of the name | No |
Any one of the first four rows settles it. Together they are conclusive without a laboratory, an acid or an assay.
Ordered by how much each one proves. The decisive tests are worth your first two minutes; the supporting ones only matter once those agree.
This is the single most useful mineral test there is and almost nobody does it. Drag the specimen hard across the unglazed back of a ceramic tile. Pyrite leaves a distinct greenish-black or brownish-black line. Gold leaves a yellow metallic smear. Chalcopyrite — the other brassy sulphide people mistake for gold — leaves greenish-black too, so a dark streak tells you it is not gold without telling you which sulphide it is.
Choose an inconspicuous spot and push firmly with a steel pin or a knife point. Gold is malleable and will take a dent, with the metal displaced rather than removed; a fragment of gold bends and flattens. Pyrite is brittle and shatters locally into angular fragments and powder. This is the property that made the mineral's nickname, and it is unmistakable once you have seen both.
At 19.3, gold is nearly four times as dense as pyrite and about seven times as dense as ordinary rock. If you can weigh the specimen dry and then submerged, the density is a hard number. If not, simply lift it: a gold-bearing specimen of any size feels wrong in the hand, and pyrite feels like a heavy but unremarkable stone.
Pyrite crystallises in the cubic system and forms astonishingly good cubes, twelve-sided pyritohedrons and octahedra, often with fine parallel striations across the faces running at right angles from one face to the next. Gold does not form cubes in nature at any size you will find in the field; it forms irregular masses, plates, wires and branching dendrites. A perfect brassy cube is pyrite, and it is a nicer thing to own than a flake of gold.
Pyrite at 6–6.5 marks both copper (3.5) and glass (5.5). Gold at 2.5–3 marks neither and is itself scratched by the coin. Do the coin test first, because it is the one that separates the soft native metals from the hard sulphides in a single stroke.
Pyrite is an iron sulphide and it decays. Older or damp-stored specimens develop a faint sulphurous smell, a whitish or rusty bloom, and eventually crumble — a process collectors call pyrite disease. Gold does none of this and never will. A brassy specimen that has gone rusty in a drawer answers its own question.
Pyrite is not faked; it is the thing that fools people by existing. The relevant deception runs the other way, and it takes two forms worth naming.
The first is 'gold in quartz' specimens sold online, where the brassy material in the vein is pyrite or chalcopyrite and the listing is careful never to quite say gold. The second is brass, gilt or gold-painted stone sold as natural gold specimens, which is cruder and fails a streak test instantly. There is also a genuine and legitimate product — cultured or lab-grown pyrite crystals — which are real pyrite and sold honestly, but a suspiciously perfect set of identical cubes at a low price is usually those rather than a Spanish mine's output.
Each of these is checked differently. The ones with their own page have enough that is specific to them to be worth reading separately.
Specimen figures rather than gem figures, for material in honest condition. Most finds are worth very little, and saying so plainly is more useful than encouraging you.
| Form | What it typically fetches | Note |
|---|---|---|
| Massive pyrite, rough chunk | $1 – 5 | Common beyond use |
| Pyrite 'sun' or dollar, Illinois | $20 – 90 | A flat radiating disc — a genuine specialty |
| Sharp Spanish cube on matrix | $20 – 200 | Size and face perfection |
| Fine multi-cube plate, Navajún | $300 – 2,000+ | Aesthetics and undamaged matrix |
| Any of it as gold | Nothing | It is not gold, and it never was |
Pyrite is priced entirely as a specimen mineral. It has industrial history as a sulphur source and essentially no bullion value, which is the disappointment the room exists to deliver kindly.
Lovenhall StoneThe tests tell you what it is. The instrument reads a photograph and offers a name to start from — then hands you back to the tile and the coin, which are what settle it.