Pyrite

Pyrite, also known as iron pyrite or Fool's Gold, is a common mineral made of iron and sulfur, with the chemical formula FeS₂. It is the most abundant sulfide mineral found in nature.

What makes pyrite special is its bright, metallic shine and pale yellow color, which looks a lot like gold. Because of this, people often called it Fool's Gold. Other old names for pyrite include brass, brazzle, and brazil, especially when it is found in coal.

The word pyrite comes from the Greek words for "stone that strikes fire," because when pyrite is hit against steel, it can make sparks. Ancient people noticed this special property long ago. Today, pyrite is often found in rocks such as quartz veins, sedimentary and metamorphic rocks, and even in some fossils. Sometimes, tiny amounts of real gold can be found with pyrite, hidden inside the mineral.

Uses

Pyrite was once used in the 16th and 17th centuries to help start early guns by creating sparks. The Kaurna people of South Australia used pyrite to start fires along with flintstone and special tinder.

Today, pyrite is used to make sulfur dioxide, which is important for the paper industry and for creating sulfuric acid. It is also used in some batteries and as a material in solar panels. Because of its shiny, gold-like appearance, pyrite is sometimes used in jewelry and decorations, especially in silver settings. It is also a popular mineral for collectors, with some of the best specimens coming from Spain.

Research

In July 2020, scientists found that by using electricity, they could change pyrite from a material that does not attract magnets into one that does. This could be useful for making things like solar cells or devices that store data using magnets.

Researchers in Ireland showed that pyrite can be made very thin, like some other special materials, by using a simple process with liquids. They used these thin pieces of pyrite together with carbon tubes in batteries, and they worked very well. Later, in 2021, they made even better thin pieces of pyrite that worked even better in batteries.

Formal oxidation states for pyrite, marcasite, molybdenite and arsenopyrite

From the view of classic chemistry, which gives each atom a formal charge, pyrite and marcasite are best described as Fe²⁺[S₂]²⁻. This shows that the sulfur atoms in pyrite are paired with clear bonds between them. These pairs are like units from hydrogen disulfide, H₂S₂, so pyrite could be called iron persulfide instead of iron disulfide. Molybdenite, MoS₂, has single sulfide S²⁻ centers, and the molybdenum has a charge of Mo⁴⁺. The mineral arsenopyrite has the formula FeAsS. While pyrite has [S₂]²⁻ units, arsenopyrite has [AsS]³⁻ units, coming from removing a hydrogen from arsenothiol (H₂AsSH). Looking at these charges, arsenopyrite would be described as Fe³⁺AsS³⁻.

Crystallography

Iron-pyrite, with the chemical formula FeS₂, shows a special cubic shape that scientists studied using special light called X-ray diffraction. It is part of a group called _Pa_3 and has a specific pattern known as C2.

In this shape, iron atoms form a special cube pattern, and sulfur atoms fit into this pattern. The iron atoms connect to six sulfur atoms, making a stretched cube shape. The sulfur atoms also connect in pairs. This structure helps scientists understand how other materials with similar patterns behave.

Crystal habit

Pyrite most often grows in cube shapes. Sometimes, these cubes grow close together to make small, round clusters that look like raspberries, called framboids. In some cases, pyrite can grow in thin threads or T-shaped crystals. It can also form shapes very similar to a twelve-sided figure called a dodecahedron, which might explain why people in Europe long ago made similar shapes for their art.

Varieties

There are several minerals similar to pyrite, including cattierite, vaesite, hauerite, and sperrylite. These minerals share a similar structure with pyrite.

Another type is called bravoite, which contains nickel and cobalt. Bravoite is not officially recognized as a mineral and is named after a scientist from Peru named Jose J. Bravo.

Distinguishing similar minerals

Pyrite looks like gold but can be told apart by a few clues. Pyrite breaks easily and has uneven or shell-like fractures, while gold bends and does not break. Gold pieces are usually irregular in shape, but pyrite often forms cubes or crystals with sharp, clear faces. You might also see lines on pyrite’s surface.

Another mineral, chalcopyrite, is a brighter yellow and turns greenish when wet. Arsenopyrite is silver white and stays the same color when wet, unlike pyrite.

Hazards

Iron pyrite can change when it meets air and water. It breaks down and can make the area around it more acidic. This is especially a problem in places where coal is mined.

When pyrite is mixed with dust, it can sometimes cause dangerous explosions in mines. To help prevent this, miners spray limestone dust to make things safer.

Buildings made with stone or concrete that contains pyrite can also have problems. As the pyrite changes, it can damage the building materials and cause them to break apart over time.

Occurrence

Pyrite is the most common sulfide mineral and can be found in many types of rocks, including igneous, metamorphic, and sedimentary rocks. It often appears as a smaller part of these rocks but can sometimes form larger pieces. Pyrite can be a part of the original sediment or form later as the rock changes over time.

You can find pyrite in places like Virginia in the U.S., and in large amounts in Rio Tinto, Spain, among other spots around the world.

Cultural beliefs

In Thai culture, especially in the southern part, pyrite is called Khao tok Phra Ruang, Khao khon bat Phra Ruang, or Phet na tang and Hin na tang. People believe it is a special item that can help keep away bad things and protect against harmful forces.