Calcite vs Quartz
| Property | Calcite | Quartz |
|---|---|---|
| Formula | CaCO3 | SiO2 |
| Crystal System | Trigonal | Trigonal |
| Mineral Class | 05 Carbonates and Nitrates | 09 Silicates |
| Mohs Hardness | 3.0 | 7.0 |
| Color | Colorless, white, yellow, orange, blue, green | Colorless, white, purple, pink, brown, black |
| Luster | Vitreous | Vitreous |
| Streak | White | White |
| Transparency | Transparent | Transparent |
| Cleavage | Perfect rhombohedral {1011} | None |
| Fracture | Conchoidal | Conchoidal |
Key Differences
- ◆ Calcite (hardness 3) is much softer than quartz (hardness 7) and can be scratched by a copper coin.
- ◆ Calcite effervesces vigorously in dilute HCl; quartz does not react.
- ◆ Calcite has perfect rhombohedral cleavage; quartz has no cleavage and breaks conchoidally.
- ◆ Calcite is calcium carbonate (CaCO3); quartz is silicon dioxide (SiO2).
- ◆ Calcite displays double refraction (birefringence) in Iceland spar crystals; quartz does not.