Breunnerite

Breunnerite, also known as brown spar^[2]: 258 (German: braunspat) is a variety of magnesite, with a magnesium/iron ratio of 90/10 to 70/30.^[1]

Breunnerite
Breunnerite from Bolzano. Italy
General
Category	Carbonate mineral
Formula	(Mg, Fe) CO 3
Crystal system	Trigonal[1]
Identification
Color	from yellowish or gray-brown to brown
Cleavage	perfect on a rhombohedron
Mohs scale hardness	4.0-4.5
Luster	metallic
Diaphaneity	translucent to opaque
Density	3.0-3.2 (calculated)

For other uses, see brown spar.

Name and history

It has been described by Wilhelm Karl Ritter von Haidinger in samples of Pfitsch pass, Zamsergrund and Großer Mt Greiner, Zemmgrund [de], two cities of the Ziller Valley, Tyrol, Austria.^[3]

Haidinger named the new variety of the magnesite in honor of Count August Breunner [de]^[4] (sometimes the family name is written as Breuner; 1796-1877), a famous collector of minerals and fossils, as well as a high-ranking government official of Austria-Hungary.^[1]

In 19th century mineralogy, as well as in mining and among geologists, breunnerite and its close analogues from the isomorphic series magnesite → siderite were more often known under the capacious morphological name ″brown spar″.^[5]: 34

Application

Breunerite is widely used in firing during the formation of raw materials for the subsequent production of refractories. When magnesium carbonate, which is part of breunerite, is brought to a temperature of about 600°C, it enters the firing process as a mineralizer, first decomposing and then reacting and forming two main compounds that act as raw materials: 2CaFe₂O₃ и MgOFe₂O₃. Breunerite produces a less pure product than a mixture of magnesia and iron oxide, but is more economical to produce.