Here's why:

* Naturally occurring: Pyrite is found in nature.

* Inorganic: It's not derived from living organisms.

* Solid: Pyrite exists in a solid state.

* Definite chemical composition: Pyrite has a consistent chemical formula (FeS2 - iron sulfide).

* Ordered internal structure: Its atoms are arranged in a specific, repeating pattern, giving it a crystalline structure.

Pyrite is often called "fool's gold" because it has a golden color and metallic luster, but it's not gold.