Siderite

Siderite is an iron carbonate mineral with the chemical formula FeCO3. It typically forms rhombohedral crystals or massive aggregates, and has a yellowish-brown to grayish-white color with a dull or pearly luster. It has a Mohs hardness of 3.5-4.5 and a specific gravity of 3.8-4.0.
Siderite is a relatively common mineral, found in sedimentary rocks and in hydrothermal veins. It often occurs in association with other iron minerals, such as hematite and magnetite, as well as with calcite, dolomite, and other carbonate minerals.
Siderite can be found in many parts of the world, including Europe, North America, and Asia. Notable deposits include the Lake Superior region of North America, the Harz Mountains of Germany, and the Trepča Mines in Kosovo.