SIDERITE on DOLOMITE, Marro Velho Minas Gerais BRAZIL (small cabinet)

Siderite is a mineral made up of iron(II) carbonate (FeCO3), deriving its name from the Ancient Greek term σίδηρος (sídēros), which translates to "iron." This mineral is an important iron ore, containing 48% iron and is free from sulfur and phosphorus. Iron can be substituted by elements such as zinc, magnesium, and manganese, leading to the formation of solid solution series like siderite-smithsonite, siderite-magnesite, and siderite-rhodochrosite.

With a Mohs hardness ranging from 3.75 to 4.25 and a specific gravity of 3.96, siderite exhibits a white streak and displays either a vitreous or pearly luster. It becomes antiferromagnetic at temperatures below its Néel point of −236 °C (4K), a characteristic that can aid in its identification.

Dolomite is an anhydrous carbonate mineral primarily made up of calcium magnesium carbonate, represented by the formula CaMg(CO3)2. The term also refers to a sedimentary carbonate rock that predominantly consists of the dolomite mineral, which is sometimes called dolostone. 

The Dolomite Mountains, located near Cortina d'Ampezzo in Italy, derive their name from this mineral. Carl Linnaeus is credited with the initial description of dolomite in 1768, while Déodat Gratet de Dolomieu later identified it as a rock in 1791, first observing it in ancient Roman structures and subsequently in the Tyrolean Alps. Nicolas-Théodore de Saussure officially named the mineral in March 1792, honoring Dolomieu. 

Dolomite crystallizes in a trigonal-rhombohedral system, producing crystals that can be white, tan, gray, or pink. As a double carbonate, it features an alternating arrangement of calcium and magnesium ions. Unlike calcite, dolomite does not dissolve or effervesce quickly in cold dilute hydrochloric acid unless in a fine powder form, and crystal twinning is a common occurrence.