The key difference between pyrite and marcasite is that pyrite has an isometric crystal system, whereas marcasite has an orthorhombic crystal system.
Pyrite and marcasite are two forms of iron sulfide minerals containing iron in a +2 oxidation state. Although the two mineral forms have the same chemical composition, they have different crystal systems.
What is Pyrite?
Pyrite is a mineral of iron, having iron disulfide in an isometric crystal system. This substance is also known as iron pyrite or fool’s gold. The chemical formula of this mineral is FeS2, while the formula mass of this substance is 119.98 g/mol. Moreover, it is the most abundant sulfide mineral on Earth.
Pyrite has a pale brass-yellow reflective lustre, which tarnishes darker and iridescent. When considering the twinning on the pyrite mineral, it shows penetration and contact twinning, and the fracture is uneven, but sometimes it can be conchoidal. This mineral is brittle, and it has a metallic lustre. In addition, the streak colour of pyrite is greenish-black to brownish-black. This substance is opaque, and it has a hardness ranging from 6-6.5 on the Mohs scale. In addition, it is a paramagnetic material.
Pyrite mineral typically forms cuboid crystals. Sometimes it forms raspberry-shaped masses known as framboids. Moreover, this substance can form shapes that are similar to the regular dodecahedral form. Although pyrite resembles gold, which leads to its alternative name, fool’s gold, we can easily distinguish this substance from native gold based on the hardness, brittleness, and crystal system. Native gold is irregularly shaped (anhedral) and pyrite is cubically shaped or multifaceted crystal shaped.
There are many uses of pyrite, including its use as a source of ignition at early times, use in producing ferrous sulfate or copperas, for the production of sulfur dioxide to be used in the paper industry, etc., as a cathode in energizers, etc.
What is Marcasite?
Marcasite is a mineral of iron having iron disulfide in an orthorhombic crystal system. It is also known as white iron pyrite because it is a different form of pyrite. The chemical composition of marcasite is ferrous sulfide or FeS2, arranged in an orthorhombic crystal system. This mineral form is physically and crystallographically different from pyrite.
When considering the appearance of marcasite, it has tin-white on the fresh surface, which darkens upon exposure to air. The fracture of marcasite is irregular or uneven, and the mineral is brittle as well. In the Mohs hardness scale, this mineral has about 6-6.5 hardness, and the lustre of this mineral is metallic. Furthermore, the streak colour of marcasite is dark grey to black. Marcasite is an opaque material.
What are the Similarities Between Pyrite and Marcasite?
- Pyrite and Marcasite are minerals of iron disulfide.
- Both have a metallic lustre.
- These minerals have iron in a +2 oxidation state.
What is the Difference Between Pyrite and Marcasite?
Pyrite and marcasite are two forms of iron disulfide minerals. The key difference between pyrite and marcasite is that pyrite has an isometric crystal system, whereas marcasite has an orthorhombic crystal system. Moreover, pyrite has a pale brass-yellow reflective lustre while marcasite has a tin-white appearance on a fresh surface.
The below infographic summarizes the difference between pyrite and marcasite in tabular form.
Summary – Pyrite vs Marcasite
Pyrite and marcasite are mineral forms of ferrous sulfide where iron occurs in a +2 oxidation state. They have a different crystal structure, which makes them different from each other. The key difference between pyrite and marcasite is that pyrite has an isometric crystal system, whereas marcasite has an orthorhombic crystal system.
1. “Marcasite.” Wikipedia, Wikimedia Foundation, 11 Feb. 2021, Available here.