RocksdayRocksday #5 · October 26, 2026
The answer was Malachite
A vivid green copper carbonate with bold light-and-dark banding. It forms where copper deposits weather near the surface.
The clues
- Type
- Mineral
- Color & luster
- Green · Silky to dull
- Mohs hardness
- 3.5–4
- Crystal system
- Monoclinic
- Found in
- Katanga, DR Congo; Ural Mountains, Russia
How to recognize malachite
- Bright green with concentric light/dark bands.
- Fizzes in acid.
- Feels heavy for a stone.
- Light green streak.
Did you know? The Malachite Room in St. Petersburg's Winter Palace is clad in about two tons of it.