Siderite

Siderite is an iron carbonate mineral with the chemical formula FeCO₃, composed of iron, carbon and oxygen. It has a Mohs hardness of 3.5–4.5, a specific gravity of around 3.96, and perfect rhombohedral cleavage.

Locality: China 🇨🇳 

The colour appears yellow through the camera lens, however it is actually brown with a green undertone.