Polymorph
Definition
Two or more minerals that have the same chemical composition but different crystal structures and physical properties.
Example
Diamond and graphite are polymorphs: both are pure carbon, but their atoms are arranged differently.
Same Ingredients, Different Cake
Polymorphs (from Greek "many forms") are minerals that have the exact same chemical formula but different crystal structures. This happens because the minerals form under different conditions of temperature and pressure. The arrangement of atoms determines the physical properties, so polymorphs can look and act completely differently despite being chemically identical.
Famous Examples
- Diamond vs. Graphite: Both are pure Carbon (C). Diamond forms under extreme pressure (cubic structure) and is the hardest mineral. Graphite forms at lower pressure (hexagonal sheets) and is one of the softest minerals (pencil lead).
- Calcite vs. Aragonite: Both are Calcium Carbonate (CaCO3). Calcite is stable; Aragonite is metastable and often created by biological processes (shells/pearls).
- Pyrite vs. Marcasite: Both are Iron Sulfide (FeS2).