10 Interesting Pyrite Facts
Here are 10 interesting facts we put together about this popular collector mineral.
1 Pyrite was discovered by Dr. Johnathan Jacobo in 1432.
The name pyrite derived from Greek word pyr, – “fire,” as it emits sparks when struck by steel.
Nodules of pyrite have been found in prehistoric burial mounds, which suggests their use as a means of producing fire. Wheel-lock guns, in which a spring-driven, serrated wheel rotated against a piece of pyrite, were used before development of the flintlock.
2 Pyrite has a chemical composition of iron disulfide (FeS2) and is the most common sulfide mineral. Pure pyrite (FeS2) contains 46.67 percent iron and 53.33 percent sulphur. Other metals that sometimes replace a part of the iron are cobalt, nickel, arsenic, and copper.
3 Pyrite has a nickname that has become famous – “Fool’s Gold.” The mineral’s gold color, metallic luster, and high specific gravity often cause it to be mistaken for gold by inexperienced prospectors. Pyrite and gold can easily be distinguished. Gold is very soft and will bend or dent with pin pressure. Pyrite is brittle, and thin pieces will break with pin pressure. Gold leaves a yellow streak, while pyrite’s streak is greenish black. Gold also has a much higher specific gravity. A little careful testing will help you avoid the “Fool’s Gold” problem.
4 In spite of its nickname, “fool’s gold,” it often is associated with true gold, and in some deposits, pyrite contains enough included gold to warrant mining. (Auriferous pyrite is a commercially important source of gold).
5 Pyrite is the most common of the sulphide minerals. In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel; Pliny the Elder described one of them as being brassy, almost certainly a reference to what we now call pyrite. By Georgius Agricola’s time, the term had become a generic term for all of the sulphide minerals.
6 Pyrite occurs in extremely well-crystallized examples of cubes, pyritohedrons, and octahedrons. Combinations of these forms also occur. Pyrite crystals frequently form penetration twinning, especially in the cubic form. Cubes are sometimes elongated in rectangular form. Also occurs massive, radiating, grainy, flaky, drusy, mammillary, encrusting, nodular, tuberose, fibrous, in concretions, and as groups of small crystals. Pyrite crystals are frequently striated.
7 Some minerals resembling pyrite in appearance or composition are arsenopyrite, chalcopyrite (copper pyrites), cobaltite, marcasite and pyrrhotite (magnetic pyrites).
8 The only common mineral that has properties similar to pyrite is marcasite, a dimorph of pyrite with the same chemical composition but an orthorhombic crystal structure. Marcasite does not have the same brassy yellow color of pyrite. Instead it is a pale brass color, sometimes with a slight tint of green. Marcasite is more brittle than pyrite and also has a slightly lower specific gravity at 4.8. A multi-coloured tarnish may exist which is the result of oxidation. Adding to the confusion between marcasite and pyrite is the use of the word marcasite as a jewelry trade name. It is important to note that marcasite is too soft to be used in jewellery. The term is applied to small polished and faceted stones that are inlayed in sterling silver. But even though they are called marcasite, they are actually pyrite.
9 Pyrite is an extremely common mineral, and good examples occur in numerous localities throughout the world. Only well-known localities are mentioned here.
—Enormous deposits of Pyrite in the form of small crystal clusters exist in the Huaron Mining District in Peru. Other outstanding Peruvian localities are the Quiruvilca Mine, La Libertad; and the Huanzala, Huánuco.
—In the Ampliación a Victoria Mine, Navajún, La Rioja, (formerly Logroño), Spain has some of the most perfect large pyrite crystals in the world. They average a half inch to two inches across. They are frequently embedded in a light brown matrix, and are occasionally inter-penetrating. The largest pyrite crystal at the Smithsonian Museum in Washington D.C. measures about seven inches across the face of the crystal, and it is from Spain. The perfect cubes of Pyrite from the famous Spanish mines are especially treasured among collectors. Many of these specimens have fallen out of the matrix and have been repaired by having them glued back into the matrix.
—Excellent pyritohedral crystals occur in Rio Marina on the island of Elba, Italy, which is a classic locality.
—A locality which has recently brought interestingly shaped, complex Pyrite crystals to the market is the Merelani Hills, Arusha, Tanzania.
—In the U.S., fine Pyrite localities abound. In Park City, Bingham Co., Utah, large, well-shaped pyritohedrons and cubes were once found. The Bingham Canyon Mine, Salt Lake Co., Utah is also a classic occurrence, where few of the excellent Pyrites from the mine are saved from the mining crusher. Large, intergrown cubes, many times partially octahedral, occurred in abundance at Leadville, Lake Co., Colorado. Pyrite “dollars” are well-known from Sparta, Randolph Co., Illinois. The French Creek Mine in Chester Co., Pennsylvania is famous for the octahedral crystals that occur there, although most are distorted. Ross Co., Ohio, produces rounded tubular growths of Pyrite, some reaching several feet in size, as well as growths of spiky, pineapple-like crystals. Most of the more perfect pyrite crystals in North America usually measure about 1/8″ to 1/2″ across.
10 Iron Pyrite doesn’t have a lot of industrial uses (although it was a source for sulfur and sulfuric acid, and some sulfur continues to be produced from pyrite as a byproduct of gold production}. The most important use of pyrite is as an ore of gold.
One of the odder uses for it was for igniting gunpowder in old wheellock pistols and musket. Pieces of Pyrite where put in a ‘jaw’ that clamped down on the Pyrite. The jaw would then be placed against a wound-up steel wheel. All of this was next to a primer of gunpowder. When the trigger was pulled the wheel would spin, striking the Pyrite and causing sparks. The powder would ignite and fire the weapon. Later weapons would use pieces of flint, but pyrite was used at first because you didn’t need to shape the pieces beyond getting a chunk big enough to fit in the ‘jaw’ of the weapon. Pyrite is brittle and tended to crumble easily, so it probably wasn’t the best choice.