What is the Difference Between Pyrite and Marcasite?

Pyrite and marcasite are two forms of iron sulfide minerals containing iron in a +2 oxidation state. Although they have the same chemical composition, they have different crystal systems and structures. Here are the main differences between pyrite and marcasite:

1. Crystal System: Pyrite has an isometric crystal system, whereas marcasite has an orthorhombic crystal system.
2. Crystal Shape: Pyrite crystals are generally equant and dominated by cubes, octahedrons, and 12-sided pyritohedrons. Marcasite crystals are usually rectangular (tabular) with wedge-shaped ends and tend to form in star-shaped, radiating, or cockscomb groups.
3. Color: Marcasite tends to be lighter in color and is sometimes referred to as "white iron pyrite". It can sometimes have a greenish tint. Pyrite, on the other hand, has a pale brass-yellow reflective luster that tarnishes darker and iridescent.
4. Streak: Pyrite's streak is greenish-black, while marcasite's streak is grey to black.

In summary, pyrite and marcasite differ in their crystal systems, shapes, colors, and streaks. While they share the same chemical composition, these distinctions set them apart as distinct mineral forms.

Comparative Table: Pyrite vs Marcasite

The key difference between pyrite and marcasite is their crystal systems. Here is a table comparing the two minerals:

Both pyrite and marcasite are iron sulfide minerals with the same chemical composition, but they have different crystal structures, making them distinct minerals.