Pyrite vs Gold: 7 Simple Ways to Tell Them Apart
Fool's gold fools a lot of people. These seven quick tests, from the shadow test to the streak test, tell you in minutes whether you have gold, pyrite, chalcopyrite or mica.
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Almost everyone who spends time near rocks eventually picks up something bright and yellow and wonders. Most of the time it is pyrite, the mineral nicknamed fool's gold. The good news is that gold and pyrite behave very differently, and you can tell them apart with a pocket knife, a piece of unglazed tile and a bit of shade.
Gold and pyrite at a glance
| Property | Gold | Pyrite | Chalcopyrite |
|---|---|---|---|
| Colour | Warm butter yellow, same in sun or shade | Pale brassy yellow | Brassy yellow, often with a blue or purple tarnish |
| Streak (powder colour) | Golden yellow | Greenish black to brownish black | Greenish black |
| Hardness (Mohs) | 2.5 to 3, soft | 6 to 6.5, hard | 3.5 to 4 |
| Response to a pin | Dents or bends | Pin slides off | Scratches into a dark powder |
| Weight | Very heavy (about 19 times water) | Moderate (about 5 times water) | Moderate (about 4 times water) |
| Shape | Rounded flakes, grains, wires | Sharp cubes and crystals with fine lines | Irregular masses, rarely crystals |
| Under a hammer | Flattens | Shatters | Crumbles |
1. The shadow test
Hold the grain in sunlight, then turn it so it falls into the shade of your hand. Gold keeps its rich yellow colour from every angle, because the colour comes from the metal itself. Pyrite and mica only flash when light hits them at the right angle, and they look dull or dark in shade.
This is the first test most prospectors use in the pan, because it takes two seconds and needs no tools.
2. The streak test
Rub the mineral firmly across the back of an unglazed ceramic tile. The colour of the powder it leaves is called the streak, and it is more reliable than the colour of the sample itself.
- Gold leaves a golden yellow streak.
- Pyrite and chalcopyrite leave a greenish black streak.
If the sample is tiny, you can skip this test and use the pin test instead, so you do not lose the grain.
3. The pin or knife test
Gold is soft. Press the tip of a pin or knife into it and it will dent, bend or cut, a bit like lead. Pyrite is harder than steel, so the point skates across the surface without marking it. Chalcopyrite sits in between: a knife scratches it, but the scratch turns into dark powder instead of a clean cut.
4. The hammer test
This one is only for samples you do not mind losing. Place the grain on a hard surface and tap it gently. Gold flattens like a tiny coin. Pyrite shatters into sharp fragments, and freshly broken pyrite often gives off a faint smell of sulfur, like struck matches or rotten eggs.
5. Weight in the pan
Gold is far heavier than anything else you are likely to find in a stream. In a gold pan, real gold sinks immediately and stays at the bottom no matter how hard you swirl. Pyrite moves around with the black sand, and mica flakes float off with the lightest material.
6. Crystal shape
Pyrite loves to grow as sharp cubes, sometimes with fine parallel lines across the faces. Gold almost never shows neat crystal faces in the field. Placer gold is usually rounded, flattened or ragged, and gold in quartz tends to appear as irregular specks, wires or leaf shapes.
If you can see a clean cube, you are almost certainly holding pyrite.
7. Where you found it
Context helps too. Gold flakes are normally found in stream gravels with black sand, or inside quartz veins. Pyrite is extremely common in many types of rock, including slate, shale and coal, and it often appears as glittering crystals spread through the whole rock. A rock that sparkles all over with yellow crystals is a lot more likely to be pyrite than gold.
Do not forget mica
Weathered mica, especially biotite, turns golden and catches light in shallow water. It can look very convincing in a creek. Pick it up and it gives itself away: it is paper thin, very light, and it crumbles or floats away when you touch it. Gold flakes are heavy and stay put.
Does pyrite ever mean gold is nearby?
Sometimes. Pyrite and gold can form from the same hot fluids, and in some deposits gold is locked inside pyrite grains as particles too small to see. That is why mining companies test pyrite-rich rock in a laboratory. For the hobby prospector, pyrite on its own is not a reason to start digging, but pyrite in quartz near known gold workings is worth noting.
A quick test routine for the field
- Do the shadow test as soon as you see something yellow.
- If it still looks good, press it with a pin. Gold dents, pyrite does not.
- For larger samples, do a streak test on unglazed tile.
- Keep anything that passes in a small vial and compare it later with known gold.
If you think you have found a significant amount of gold in rock, a local assay laboratory can confirm it and tell you exactly how much is there.