Malachite (a hydrated copper carbonate) is unmistakably green, typically forming botryoidal and banded masses, often alongside blue azurite. Its vivid green, concentric banding, and reaction with dilute acid are diagnostic.
Field identification workflow
- Start with the banding: cut or broken botryoidal malachite shows concentric light-and-dark green rings that almost nothing else imitates.
- Streak light green — darker green specimens leaving a pale green streak is the expected result, not a failure.
- Test with dilute acid: it effervesces like the carbonate it is.
- Check for blue: azurite on the same specimen is corroborating evidence, since the two copper carbonates grow and alter together.
A note for lapidaries
Malachite is soft, sensitive to acid and heat, and its dust is a copper compound — cut wet, and wash up before lunch. The Rock Tumbler and Lapidary Equipment Safety standard applies.