The Difference Between Gold and Pyrite

Whether you’re a pirate, a prospector, or pretty much anyone else, you’d probably love to get your hands on some gold. However, you may have heard of a common pitfall — accidentally uncovering “fool’s gold”, instead. What’s the difference, anyway?

What is gold?

We all know what gold is, right? What makes it so special? Well, the main reason we collect it — and pay so much for it — is that it’s very rare, and jewelry made out of it looks very pretty. We often mix gold with other metals to change the color slightly (e.g., “white” gold is mixed with platinum.) Gold is the most malleable of all metals, so it’s easy to change its shape. It’s also useful because it doesn’t rust, and is a good conductor of electricity. Famously, we have a huge stockpile of gold in Fort Knox in the U.S., which is used to “back” the value of the American dollar.

What is pyrite?

Pyrite — often called Iron Pyrite, and known famously by the nickname “fool’s gold” — is a common sulfide mineral that looks similar to gold when it’s in the ground. Pyrite has actually been quite useful throughout history: we’ve used it in early firearms, to make other chemicals like sulfates, and in crystal radios. Today it’s still useful for making some kinds of batteries and jewelry, and we’re looking into using it to make solar panels. The world’s largest importer of pyrite is China, so if you found a new mine, you could try to sell it there!

How can you tell the difference?

  • True gold is a reddish-yellow color, while pyrite is described as “brass yellow”.
  • Iron pyrite will quickly decompose in Earth’s atmosphere. Gold, famously, is highly resistant to oxidation.
  • Gold is soft and malleable (2.5 on Mohs hardness scale), while pyrite is brittle and hard (6-6.5 hardness). You can scratch gold, but not pyrite, with a pin (don’t use your fingernail, though — that’s a myth).
  • Pyrite crystallizes, often into pretty cubes. Gold is usually found as an amorphous blob shape.
  • Gold is a pure element (Au); Pyrite, however, is a metallic compound (Fe + S2).
  • Density: Pyrite (4.9 g/cm3) is much, much lighter than gold (19.3 g/cm3).
  • Scrape: if you scrape gold on a piece of white porcelain, it will leave a yellow streak; pyrite’s streak will be black.

With these facts in mind, it should be easy for you to tell the difference between fool’s gold and real gold. The fastest test is probably to weigh it and see if it’s heavy enough to be real gold or to try to scratch it with anything harder than 2.5 but not as hard as 6 on Mohs hardness scale. While gold often is found in small amounts in the same locations as iron pyrite, it’s probably not enough to be worth the trouble of mining it.

Is it really that easy to be fooled?

Several times in history, prospectors have been fooled by pyrite, wasting countless hours and energy mining the stuff while thinking they were going to be rich. For example, around the time that Europe was colonizing and exploring the New World, a privateer named Sir Martin Frobisher found a pyrite mine in Canada and shipped about 1,600 tons of the ore back to England, only to discover that it was going to be used to pave roads. Always check your “gold” before you get too excited!