Cubes, naturally.
Pyrite, Meaning, Properties, and Facts
Iron sulfide · FeS2Mohs 6 to 6.5Cubic
Pyrite is iron sulfide, the brassy yellow mineral nicknamed fool's gold, and it grows natural cubes so sharp they look machined. Below: its properties, where it is found, its crystal shapes, how to tell it from gold and from fakes, care and the meaning people give it.
What is pyrite
Pyrite is the most common sulfide mineral on Earth: one iron atom for every two sulfur atoms. Its name comes from the Greek word for fire, because it throws sparks when struck against steel, and people used it to start fires and later to fire wheellock guns. The nickname fool's gold came from prospectors who mistook its brassy shine for gold, though pyrite sometimes holds tiny amounts of real, invisible gold, as the Wikipedia pyrite article explains.
Pyrite properties
Pyrite properties make it easy to identify once you know them: it is heavy, hard enough to scratch glass, brittle, and it leaves a greenish black streak on unglazed porcelain (full data on Mindat's pyrite page):
| Mineral | Pyrite (iron sulfide) |
|---|---|
| Chemistry | FeS2 |
| Hardness | 6 to 6.5 on the Mohs scale |
| Crystal system | Cubic (isometric) |
| Luster | Metallic |
| Streak | Greenish black |
| Specific gravity | About 5.0 |
| Main localities | Spain, Peru, Italy (Elba), Colorado and mining districts worldwide |
| Water safe | No soaking: it can rust and decay |
| Sun safe | Yes |
Where pyrite is found
Pyrite is found almost everywhere: in coal, shale, limestone, hydrothermal veins and metamorphic rock. The famous specimen sources are Navajún in La Rioja, Spain, where near-perfect cubes grow inside soft marl; the mines of Peru, known for big, bright clusters; and the island of Elba, Italy, known for twelve-sided crystals. Colorado's old gold districts are full of it, often in the same quartz veins as the gold; the Colorado crystals and collecting hub covers where people collect in the state.
Pyrite crystal shapes
Pyrite crystal shapes are its party trick. It grows as cubes with fine parallel grooves (striations) that run at right angles on neighboring faces, as pyritohedrons with twelve five-sided faces, as octahedrons, and as clusters and glittering crusts. It also replaces shells and wood in fossils, which is how pyritized ammonites form. A natural pyrite cube is not cut or polished: those flat faces and sharp edges are simply how the atoms stack.
Pyrite vs gold
Pyrite vs gold is easy to settle with three tests. Gold is soft enough to dent with a pin and bends instead of breaking, while pyrite is hard and brittle; gold leaves a gold-yellow streak and pyrite a greenish black one; and gold is about four times heavier for its size. Gold rarely forms visible crystals, so a striated cube is a giveaway.
How to tell if pyrite is real
How to tell if pyrite is real: check weight, streak and surface. Real pyrite feels heavy for its size, cold and hard, and its brassy color runs all the way through; painted or plated stones show a different color underneath a chip. Watch for loose cubes glued onto rock, resin casts that feel light and warm, and rainbow pyrite that has been coated. Some iridescent pyrite is natural, such as the rainbow pyrite from Russia's Volga region, so ask the seller what you are looking at.
Pyrite care: water and sun
Pyrite care is about keeping water away from it. Pyrite can go in water for a quick rinse, but soaking or damp storage starts pyrite decay: the iron sulfide reacts with moisture and air to form rusty stains, white powder and sulfuric acid, and fine-grained pieces can crumble. Dry it right away, store it somewhere dry, and keep it out of crystal elixirs, since some pyrite carries traces of arsenic. Sun is fine. See water safe crystals for more.
Pyrite meaning
Pyrite meaning, in crystal lore, is money and luck, because it looks like gold, plus protection. That is belief, not chemistry, and pyrite benefits sit in the same box. The real history is better: the Maya and other peoples of ancient Mesoamerica polished pyrite into mosaic mirrors, and pyrite was later roasted to make sulfuric acid and used as the detector in early crystal radio sets.
Pyrite price and value
Pyrite price and value depend on crystal quality more than size. Sharp, undamaged cubes and clusters, especially natural cubes still sitting in their rock, cost more than dull or broken pieces, and classic localities add value. Pyrite is common, so small raw chunks and tumbled stones are inexpensive, and a glued or painted piece is worth little.
Pyrite for sale
Pyrite for sale on geoslut arrives in drops: each piece is one of one, photographed in daylight and labeled with its locality, and the list hears about every drop first.
Pyrite FAQ
Is pyrite magnetic?
Pyrite is not magnetic enough to notice: a fridge magnet will not lift it. A brassy stone that sticks to a magnet likely contains a magnetic iron mineral such as pyrrhotite or magnetite.
Is pyrite water safe?
Pyrite is not water safe for soaking. A quick rinse is fine if you dry it at once, but long contact with water or damp air makes it rust and decay.
How much is pyrite worth?
How much pyrite is worth depends on crystal quality, not weight: common chunks are inexpensive, while sharp natural cubes and bright clusters from classic localities sell as collector specimens.
What is pyrite used for?
Pyrite was once used as a source of sulfur and sulfuric acid and to strike sparks in wheellock guns. Today it is mostly a collector's mineral, and in mining it is a problem, because its breakdown causes acid mine drainage.
Sources
- Pyrite, Mindat
- Pyrite, Wikipedia
- Pyrite, Common Minerals, University of Minnesota