The mineral Siderite is an iron carbonate (FeCO3). The iron content is 48 % and it van be more or less rich in manganese. It is commonly found in hydrothermal veins and used as an iron ore, but not extensively, since occurrences are generally small scale. It crystallizes in the trigonal system and the crystal habitat is usually rhombohedral. Color ranges from yellow to brown-red as in this specimen, but also green hues are common. The white mineral in this sample is calcite. Actual width is 18 cm and sample is from Madan, Bulgaria