How to Tell Pyrite Apart from Gold?

In 1576, Martin Frobisher believed he had struck gold. This English explorer and sanctioned pirate — authorized by the crown to seize treasure from enemy ships — was on a mission to discover the Northwest Passage, the elusive Arctic sea route that connects the Atlantic and Pacific Oceans.

Instead, Frobisher stumbled upon Labrador, Canada, and what is now called Frobisher Bay. Weeks later, he sailed west and arrived at the icy Baffin Island, where he collected a mineral sample that appeared to contain gold. However, upon closer inspection, the Royal Assayer identified the glittering fragments as pyrite — famously known as 'fool’s gold.'

Undeterred, Queen Elizabeth’s traders sent Frobisher back to Baffin, where he collected and shipped 1,400 tons (1,270 metric tons) of ore. Most of it turned out to be useless, with the gold content in a few tested samples barely reaching five to 14 parts per billion.

Despite his desire to leave Baffin and resume his explorations, Frobisher spent years fruitlessly searching for Arctic treasure. All of this was caused by that pyrite.

Elements and Compounds

Captain Christopher Newport might have understood the frustration. As the leader of Jamestown, England’s first lasting colony in North America, he repeatedly fell for the New World’s 'gold,' only for it to be — you guessed it — pyrite.

So let’s say you’re a prospector, or perhaps an eager field geologist. How can you spot pyrite's deception?

Before we dive into that, it might be useful to first clarify what pyrite actually is.

Real gold is a chemical element, a substance that no simple chemical reaction — whether through electrolysis or heat — can break down. If you’ve got a periodic table nearby, find gold nestled between platinum and mercury.

Gold’s chemical symbol is "Au" (from the Latin word for gold, "aurum"). A fun way to remember this is to chant, "A! U! Give me back my gold!" For added amusement, try saying it with a Brooklyn accent.

Pyrite is distinct. Unlike gold, it's a compound composed of two elements: iron and sulfur. This is why it’s often called "iron sulfide."

Scientists express pyrite's chemical composition as "FeS₂." This is because iron and sulfur’s symbols are "Fe" and "S," respectively. Each pyrite molecule contains one iron atom and two sulfur atoms.

Playing Rough

Distinguishing gold from pyrite isn't all that tricky if you know what to look for. Ever watched the Olympics? If so, you’ve likely seen world-class athletes biting their gold medals in front of the cameras. (It happens a lot.)

This tradition stems from the old belief that biting gold coins could reveal whether they were fake. The idea was that a high gold content would leave bite marks behind.

The reality is a bit more complex, but the tradition is based on some truth. On the Mohs' scale, which measures the hardness of minerals, gold ranks between 2.5 and 3. As far as elements go, it’s relatively soft, meaning a gold nugget can be scratched easily with a pocket knife.

Pyrite holds an advantage here; it's a bit tougher, scoring between 6 and 6.5 on the Mohs' scale. Forget about knives; you’d need a sturdy metal file to scratch this stuff.

Steel hammers are another tool that can reveal the truth. Strike some pyrite with one of these and it’ll send sparks flying. If you keep at it long enough, the pyrite will break apart and eventually turn into powder.

None of this happens when you strike gold with a hammer: No sparks, no powder. Instead, you’ll probably just flatten or expand the sample. Gold isn’t just soft — it’s also malleable.

See How I Glitter

Visually, both minerals share a yellowish tint, but gold’s hue is subtler and less brassy. Additionally, gold doesn’t form cube-shaped crystals like pyrite often does. Most of the gold found in the wild is in the shape of either flakes or irregular nuggets.

Gold will leave a yellow streak when rubbed on porcelain or white ceramic tile. In contrast, if you try the same test with pyrite, it’ll leave a darker, greenish-black streak.

Still unsure? Trust your sense of smell. While gold is virtually odorless, pyrite gives off a faint scent that’s reminiscent of rotten eggs. (That’s the sulfur talking.)

Things can get tricky because gold and pyrite sometimes appear together in the same deposits. Remember, Frobisher’s ore did have some real gold in it — though in a minuscule quantity.

If "real" gold continues to elude you, don’t give up hope. Fool’s gold still has its uses. As mentioned earlier, it can be struck to create sparks, which can start fires. In ancient and prehistoric societies, this made pyrite a prized material. In fact, the word "pyrite" comes from a Greek term meaning "firestone."

Tomorrow might bring a fresh appreciation for iron sulfide. In 2020, researchers from the University of Minnesota used electric voltage and an ionic solution to successfully convert pyrite into a magnetic material. This discovery could pave the way for affordable, sulfur-based solar cells in the future, giving fool’s gold a promising role in the green energy sector.