“Gold, I found gold!,” you shout to your friends. You quickly imagine all the things you are going to do with your newfound wealth. Then reality sets in, and you are embarrassed to discover that you have been tricked by the mineral pyrite, also known as fool’s gold. Take heart, you are not the first person (nor the last) to be fooled by pyrite. Even Captain John Smith (of Pocahontas fame) mistakenly sent an entire shipload of pyrite to London in the early 1600s, while exploring the Chickahominy River for a waterway to the Pacific.
How can I tell the difference between gold and pyrite (fool’s gold)?
Visual clues -
- Color: Gold and pyrite both have a brilliant metallic luster, but are different tones of yellow. Gold is golden to silvery yellow, whereas pyrite is a pale to medium brassy yellow that sometimes tarnishes.
- Shape: Gold usually occurs in nuggets or very small flakes, sheets, and shapeless grains. Small cubic and octahedral (two pyramids with bases joined) gold crystals are very rare. Pyrite crystals commonly form cubes, octahedrons, or pyritohedrons (twelve irregular, pentagonal or five-sided faces), frequently with striations (parallel lines) on the crystal faces. Pyrite can also occur as shapeless grains.
Physical tests -
- Hardness: Scratch the mineral with the blade of a pocket knife. Rub off any loose powder to see if the mineral has been scratched. Gold is much softer than pyrite and can be cut. Pyrite cannot be scratched. (Beware – chalcopyrite looks similar to pyrite, but is softer and can be scratched with a knife. It is a very brassy yellow, often with a bronze or iridescent tarnish.)
- Odor: Rub the mineral vigorously with a hard object. Gold has no odor, but pyrite gives off a sulphurous smell (like rotten eggs).
- Malleable: Strike the mineral with a steel hammer. Gold will flatten or change shape without breaking. Pyrite will give off sparks.