Siderite

An iron carbonate (FeCO3), siderite occurs in sedimentary deposits, hydrothermal veins, and as a replacement mineral. It crystallizes in the trigonal system, forming rhombohedral crystals with curved faces as well as botryoidal masses, and shows a vitreous luster, a white streak, perfect rhombohedral cleavage, and a conchoidal fracture. Colors range through yellowish-brown, gray, brown, and greenish, with a Mohs hardness of 3.5 to 4.5 and a specific gravity from 3.83 to 3.96. Siderite is an ore of iron, though less economically significant than hematite and magnetite. Its rhombohedral cleavage and curved crystal faces recall dolomite, but siderite is markedly denser owing to its iron content.

Siderite is an iron carbonate mineral that occurs in sedimentary deposits, hydrothermal veins, and as a replacement mineral. It is an ore of iron, though less important than hematite and magnetite.