Siderite
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Siderite is a mineral composed of iron carbonate. Its name comes from the Ancient Greek word σίδηρος, meaning "iron". A valuable iron ore, it consists of 48% iron and lacks sulfur and phosphorus. Zinc
Harvard Museum of Natural History. Siderite. Gilman, Eagle Co., CO 2012 07 20
Siderite from Redruth, Cornwall, England
Siderite crystals with galena and quartz. Size: 6.2 cm × 4.1 cm × 3.6 cm (2.4 in × 1.6 in × 1.4 in)
Disc-shaped, brown siderite crystals perched upon chalcopyrites
Concretion
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A concretion is a hard and compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or sphe
Siderite
…and is associated with barite, fluorite, galena, and others. It is also a common diagenetic mineral in shales and sandstones, where it sometimes forms concretions, which can encase three-dimensionally preserved fossils. In sedimentary rocks, siderite commonly forms at shallow burial depths and its elemental…
Concretions in Torysh, Western Kazakhstan
Concretions with lenticular shapes from an island in the Vltava river, Prague, Czech Republic
Marlstone aggregate concretion, Sault Ste. Marie, Michigan, United States
Concretion rock with white core from the Middle Jurassic of Iran